Can't pay for wat I don't know

I have a contract with MTN wich is going to expire on the 11October so they are telling me to pay R555.00 wich t know abt. They r saying Absa send a duplicate receipt wich they send bek since they dnt accept duplicates wich I wasn't aware of. They stopped deducting money from my account wich forced me to go and pay cash@absa. I'm suppoz to pay R179.00 this coming month only then my contract wth them will be over. Pliz help me. I was very loyal to their conditions but they r treating me otherwise. A consultant called me after I went to mtn to tell them that they should put me to pay as you go.