Violated and abused by MTN

I even lack the words to describe how disappointed i am with mtn . Long story short . I have a contract that expired in July . August i got debited 5 times the amount . To be exact i got debited 1600 for a 299 contract . As a consumer i feel violated and abused because they were supposed to inform me that i needed to terminate the contract before it expires. Fast forward , I've been trying to get through to MTN retention department with no success . All i get when i phone 135 all they can say is my matter has been escalated and they cant give any further feedback or turn around time , i even tried trued communicating with MTN via twitter but they are so unhelpful . I feel so helpless and im scared that next debit order date they will debit my account again .