Send them an email with your concerns about this matter. If they don't respond or don't help, I'd advise you to go get an attorney, or threaten in the letter to do so. This may end up in small claims court-- also, when you signed up, they usually show you a coverage map. If you were around a carrier's area that could be counted as roaming, why would they let you continue & sign up for your service. They would know that they were going to be paying an erroneous/heavy amount of fees to that carrier for your use of their tower. Once they realized that you were using the other towers too much, you were kicked off, which is their policy. BUT! They shouldn't have charged you 2 $200 fees. The standard fee for cancelling a contract with T-mobile (or was when I worked there) was 175 for two non-smart phones a piece.
You have a strong case of something here, and it's definitely illegal. I would really advise you to contact them, but if nothing is handled and only a partial discount is offered to you, fight back and tell them you will seek legal action should they decline to help. If this doesn't go to get you the charge removed, actually seek the legal action. In my case, I had this happen with Verizon over a ring-back tone purchase which had never happened. They claimed I owned quite a fee, and once it was disputed with them, they got rid of their charges.