Abused by Cell c

My worst regret is taking up a data contract with cell C . I took a 2 year data contract with cell C for R89 and after the contract expired something I forgot to go close it but assumed they will continue keeping me on my previous R89 plan but never they started debiting exorbitant amount of money in my account close to a thousand rand without my approval then when I realized my money missing I went to close the account but after two months. , meaning they going to deduct the money while I'm not using their data. Next thing im handed over for collection . Then I paid their dues and as I speak my name is still on it. No letter of payment.