Tmobile activated a line with no permission, and have not refunded me.

Hello I am very upset and disappointed by the customer service we have received regarding this issue.  We have our account on a military suspension while we are overseas, but we were still paying for one phone back in the states for my sister.  Once it came to closing the phone line we closed the phone line but for some reason Tmobile opened my military suspended line and had been charging me for months until I caught the charges.  Now they had been charging for about 7 months and it came out to ver 500$ that they took from my account for a line we never authorized for them to open and a line that had never been used.  We have opened MULTIPLE investigations Since the middle of July and have received no response regarding our issue.  We are very upset and highly disappointed with the lack of communication.  We have been offered credit on our account which we continually decline because we will NOT be returning back to T-MOBILE once we return to the states.