Cell C debit orders

Just sharing my frustration of Cell C. A mobile phone company in South Africa.

It is the 3rd time in about 5 months where there is money taken from my FNB account with Cell C references. It started of with R 1300 (two times), but the last one is more than R7300. Everytime I have to phone the bank to reverse the debit order. This is becoming troublesome, and apparently Cell C does not know of this. I never had a Cell C account. What to do?