T-mobile charging me after cancellation

This reminds me of what happened to me with Verizon back in the early 2000's.  I renewed after my 1 year at the 'corporate store', after waiting nearly an hour.  On Xmas morning (a couple days later) we went to use it .. and it was a message stating to visit Verizon as the phone was assigned to a different address/number.  Returned and cancelled device within the 14 day 'at the store', with cancellation paperwork.  End of the month … a bill.  Contacted VZW, and they claimed they hadn't received any cancellation.  Went to the store - they claimed it was sent to VZW and was returned, and I shouldn't worry.  Next month … another bill with 2 months.  Corp claims they haven't received, and store claims it was cancelled, then comes a notice from collections.  I contacted BBB, and never heard from VZW or collections again, and no hit on my rating.  Similarly, I have never gone to Verizon since.