Continued billing after cancellation of a telephone line

1. I cancelled a number on the 30th August to be terminated 31st September. I received a cancellation email and a reference number. 2. However, in October I was billed again. I called and was given an incident number as my account was now terminated. I asked the money to be refunded. 3. Now its November and I've been billed again. I called and was given no incident number but was told that I will be refunded but have to wait until the end of November and then I'll have to send in a bank statement before they'll refund me. they will not refund me with interest. I will not do business with them again.