My question involves collection proceedings in the State of: California

Hi, I recently got a phone call from a law-firm/collection-agency, claiming to represent a toll-road. They tell me that a few years ago they took a picture of my license plate and that I owe them over $100 for a toll charge and collections fees. How can they come after me year after the fact and charge me so much money for something I wasn't even aware of?

The car in question was sold for scrap (I assume it became scrap because it was too expensive for me to repair it) a couple of years ago. They told me I would need to prove that I didn't own the car at the time, which I don't have any records to do, I can't even double check to see if the license plate they claim to have a photo of was my license plate because I no longer have any records for the vehicle. Soon after I sold it I left the country in a state of economic hardship and when I returned had nothing more than my suitcase. So getting records like the receipt from the junk company I sold it to, or even knowing the date or license plate is something I'm simply don't have records on.

So... I was figuring that if I can't prove that I didn't own the car back then (the tow truck driver taking it away told me they would handle things with the DMV and all I had to do was sign his receipt), perhaps I can at least get this ridiculous collection charge lowered to the original toll amount. Is it even legal for them to charge me a hundred+ dollars for something I have never heard of, never received any documents on or a bill for? I once had a credit card company tell me that since I didn't get the bill (they sent it to the wrong address) that they were not allowed to charge me a late fee. They never sent me any paperwork, they told me they have an address for me at my dads house, which is absurd because I've ever lived there but I did have the address on my credit report because I redirected my credit-card statements to it back when I left the country so that I would have a US address assigned to my accounts.

Long story short, What can I do? Is it even legal for them to charge me for something I'm just now finding out about over the phone? and still have seen no documented proof of? The only reason I think they are legitimate is because I called the toll road company and they confirmed that the collection firm does work for them, so it can't entirely be a scam can it? What power do I have to get this expelled from my credit report as a collection and how can I eliminate this ridiculous $100 charge for what must have been like one dollar when it occurred?