My question involves a child custody case from the State of: Washington

Really looking for some direction and help, PLEASE!

Let's start at the beginning... My ex and I have 2 children together, a 14 year old and 11 year old (ages now). I have been paying for a cell phone for the 14 year old to have for about the last 6 or 7 years. This started because the ex was controlling the conversation I was having with them when I had to call her phone to speak with them. I mean should would tell me not to say certain things to them about their day, ways I say it, a ton. And none of this involved her, I mean to say I would ask if they had anything important in their day going on and she was upset because she didn't want them to feel like everything in their day wasn't important and would get on the phone and stop the conversation.

Fast forward, she took the phone away a few weeks ago. The phone was a replacement phone she bought off craigslist, I had been paying the monthly plan in my name and so I let it go since she officially owned the phone itself. Ok, whatever. She then told me that she was going to get the 14 year old a cell phone that she can only use while with my ex. Ok, still no big deal, kind of because what 14 year old wants to have 2 cell phones and tell her friends that they have to call one number some days and another number other days? So I offered to just take the phone number that has been associated with the 14 year old and use that for her phone since all of her friends already have it, as long as she can take that phone with her everywhere, but the ex said no and that the only way the 14 year old can have a cell phone while with me is if I pay for a phone that she has on my time and that phone would not be allowed when not with me.

I understand that whether the kids have and use the phone 1 day a year or every day of the year I would be paying the same monthly price. But the ex is just trying to control everything and punishing our child to gain control over me. An actual thing she said to me was, "this isn't about her, this is about you" in regards to the cell phone.

Is there anything I can do, any ideas, ANYTHING? I don't know if there is any legal advice that can be given, or even just any advice about how to handle this. I have 14 days to return the new cell phone, I just have no idea what to do.

Current parenting plan says nothing about cell phone usage. I have the children every other weekend during the school year with a midweek visit the week they are not with me and have them every other week during the summer.

Thanks for any advice!