OnStar In-vehicle Wifi Not working, But Data plan expired, and still being bill for service?

I have the same issue with my equinox, had a postpaid plan with At&T wireless for the entire 8 years i have owned my car, all of a sudden OnStar wants to say it's not active and disconnect it. for over a year i was paying for a connected car and unable to use it because of OnStar's update. I have gone back and forth for months, even fixing it in March of this year, only to be told today 3 months later because of an update in plans it's been disconnected again and i have to get a data plan through OnStar. I can only guess it hasn't been working for a year, but could've been longer. There was no notice that my postpaid plan was no longer accepted by OnStar. Between countless calls between reps and different departments and At&T never hearing anything like this before, being hung up on.  What is the point of evening having a service I can't use. I'd make it a point to stay on OnStar's ass to get this resolved