Trying to cancel Cell C account for over 2 years now.

I've been a customer of Cell C and had a few contracts with them for many years and started having a lot of problems lately. One after the other I cancelled al my accounts but still had one data account that was still active. I tried about 4 times to cancel it and every time the consultant assure me that it is cancelled but then they phone me in three months time and say that I owe them R1650. I then pay it and try to cancel it again and then the same happens in 3 months. I pay again and try to cancel it and the same happened again after 3 months. This went on for 2 years now and I don't receive any data at all. They just phoned men now again and told me I owe R2000. It is still not cancelled. I really do not know what to do.