Procedure not followed.Credit record now *****ed

Got an Ipad Mini on the 22 April. I took it back to MTN Menlyn on the 29 April after seeing that it in fact doesn't work like a tablet. I was helped by a lady called Marilyn and she assured me that every thing will be sorted, the contract will be cancelled and I will have to start a new one. Nothing happened until month end of May when MTN sent a Statement that I owe them money. I called both MTN Menlyn and Summer mobile and they all assured me again that everything will be sorted. They debited my account for the Ipad that I returned and I angrily went to the bank and reversed the transaction. Until today no one from Summer mobile and MTN Menlyn contacted me and I just got another bill form MTN which I will gladly reverse if the money is debited again but I am worried about my credit record because this guys are so quick to put their clients in the bad payer's list. MTN MENLYN PLEASE SORT THIS MESS OUT NOW.