Daylight Theft

I had an account in errors, which I paid off. The call center agent kept trying to convince me to keep the number even after I said multiple times I do not have the number and had lost the phone years ago and wanted to clear all debt. I eventually after repeating myself that I do not wish to be moved to prepaid or keep the number, I later received a sms telling me Ive been moved to prepaid. Im now being charged again for a number that has been inactive for over 2 years! Ive tried calling all available helpline numbers and either get hung up on, or being told the number is not on the system or they do not assist prepaid numbers.