Fraud: Friend Replaced a Cell Phone on My Account Without Permission

My question involves personal property located in the State of: Michigan

I had a friend who I added to my T-Mobile family plan, she paid a portion of the bill as well as $25/mo toward the cell phone she was using, which still carries a balance of $575 on my line of credit (minus the $100 I've paid since the falling out). FYI: With T-Mobile you either buy the phone outright or pay monthly payments divided over 24 months, she was doing the latter, and until the balance was paid off, the phone still belonged to me. We had a falling out after I discovered she broke her phone, a Samsung Galaxy S4, and then called T-Mobile pretending to be me to authorize herself to purchase a new phone after I told her she couldn't do so until she paid off the Galaxy S4. Roughly 8 minutes after this phone call ended, she had entered a T-Mobile store and "purchased" an iPhone 5s, basically she paid sales tax and added $750 onto my line of credit, without my permission. I confronted her, demanded she return both phones to me and immediately blocked her phone line, blocked the IMEI #'s for both phones and added an extra pass-code to my account so she couldn't do anything further. This happened late on a Friday evening, so the following Saturday morning I went to the police and filed a report. I told them I wanted to press charges for identity fraud and possession of stolen property. They spoke to her and basically informed me that even though I had proof that she called from her phone line pretending to be me to authorize herself to buy the iPhone, and then bought the iPhone on my line of credit, she can just say I allowed her to do it. My argument: why wouldn't I just authorize her myself, from my phone line, which is the main account phone number, or go with her to the store to get it? I felt like there was enough to go on, but he insisted there wasn't. She ended up returning the iPhone when he threatened to arrest her if she didn't, and I was luckily able to return it to T-Mobile based on the circumstances.

Here's where things get sticky, the Galaxy S4: I found out her boyfriend took it to a cell phone repair shop and sold it to them for $170, the shop owner turned around and repaired it for $95 and then sold it to a third party. Prior to selling the phone to the repair shop, her boyfriend signed a contract stating he was the owner, that it wasn't stolen, and that if the IMEI came back blocked, he would face prosecution for selling stolen property. I found out after the fact that they sold the phone two days before I confronted her, and even though it wasn't reported stolen at that point, it was still my property. I also found out the shop owner had sold the phone to the third party on Friday morning, roughly 12 hours before I blocked the IMEI. On Saturday, the angry 3rd party returned the phone for a full refund, and the angry shop owner contacted her boyfriend and started making threats, and finally midday Sunday, they gave the angry store owner my phone number after lying to him saying that I was filing false police reports, that I had sold the phone to them, and that they had my permission to sell it (none of that even made sense, if I sold it to them, they wouldn't need my permission to sell it!) I immediately told him I was busy, to call back in 15 minutes, and in that time I downloaded a phone call recorder app, set it up and waited for the call. I have about six recorded phone calls between us, with the guy degrading me, threatening to come after ME, followed by me firmly standing my ground and informing him that he's knowingly holding onto stolen property, that it's a crime and he needs to turn it over to the police. There are even instances where I said I was coming out there to get my phone and he told me he would only give me my phone if I bought it back from him, that he's a business owner trying to earn a living and he can't just give things away for free. I immediately contacted the officer -- had to leave a message because he was off Sunday and Monday, and when he got back with me Tuesday, I explained the situation and he didn't seem phased by it, he just said he would call the girl and again suggested if I didn't get the phone back that I could go after her in small claims! I called the police department in the city where the cell phone repair shop is located to see if they would budge and they told me I had to go through the original officer who I made the report with -- the guy who didn't care. Next thing I find out, the shop owner is trying to negotiate a deal with the boyfriend to sell the phone back so he doesn't lose any money or have to go to court! He started sending me text messages about this, all of which I urgently relayed to the officer, all of which got ignored, I mean the officer would call me back, but he would skate around the details and kept insisting it would be much easier if I just took it to small claims court. The last conversation I had with the shop owner was heated, where I was urgently pleading with him not to sell it back to the people who stole it from me, and him insisting it wasn't his problem, that we could work it out without him... well guess what? He sold it back to them and they sold it to a place that buys blacklisted IMEI's and unlocks them!

Why is the officer being so reluctant to take any action when I have all this proof, and when crimes are being committed left and right and being reported to him, doesn't he have an obligation? Why isn't he pushing this further so charges can be brought against her?

Can I report this higher up and have something legal done about it? I live in a township, had to go to the county sheriff's sub-station that isn't open to the public, you have to call dispatch and meet an officer there who happens to be in the area, so where would I even go, the state police? I don't even care about getting the officer in trouble, I just want to keep the ball rolling and have charges brought against her, she was in possession of, sold, and resold $575 worth of stolen property!

Am I allowed to go after the shop owner in any way, either filing a police report/pressing charges or suing for the $575? I have e-mails and text messages from the girl and her boyfriend saying they sold it to this guy and that they gave him my number and text messages from the store owner pertaining to having possession of the phone. I don't think I can get anywhere with the recorded phone calls, because I didn't tell him he was being recorded, the whole point was just for my own protection because of the way he verbally attacked and threatened me the first time I answered his phone call. The best part of it all is as he was refusing to give it back or turn it over to the police, and in between degrading and threatening me, he was insisting I had to go with him when he files charges against them... maybe he smartened up and realized he would be setting himself up to fail that way, and that's why he sold it back to them!

Thanks in advance!