Inappropriate cancellation

Cancelled my 1 MTN cellphone contract and MTN decided to cancel my entire contract and charge a cancellation fee. I then informed them i just wanted 1 contract cancelled not the entire account. I am now sitting with a cancellation fee that keeps increasing with a cost of R1000 a month yet the account is suspended as i cannot afford to pay an amount of R18000 over the period that MTN is asking for payment. I don't get the proper assistance.