refund runaround

I switched all my lines over to a different carrier months ago and keep getting a billing summary from T-Mobile showing a credit of $37.72. I have called them about 6 times now trying to get my money refunded with no luck. The first time, back in December, I was told they would credit my original payment method. I never received it. Called again in January and they said it couldn't go back to my credit card because it had been over 90 days since I had service. They told me they would issue a gift card. Never received it. Called back today and they still didn't know what was going on. Said that the request had been declined but could not seem to tell me why. Asked to speak to a supervisor 3 times and all 3 times I was disconnected with no call back even after giving them my number in case we got disconnected. I am beyond fed up. I spent over an hour on the phone with them today alone and got nowhere.