Ka Franc vs. T-Mobile

For the past six months, I have stopped using my T-Mobile account because I switched providers. I have called customer service multiple times to cancel my account and each time they assure me they will do so if I just settle that month's balance, which I do. And then I get another bill the following month. When I call back, I get another representative who says there is no record of the previous representative canceling my account. I've tried asking for a confirmation email but they say that they can't send one.

This is incredibly frustrating because I am forced to pay despite not using my account and explicitly telling them that I want to cancel my account.