Poor service skills by MTN

Hi, I took a cellphone contract with MTN and I skipped two months payment so when I enquired with MTN I was told that my outstanding balance was R1300. I made R800 payment on the 30th of April at the store and I was told my outstanding balance is R500. A week later I received a call from VERICRED, I was told my account has been handed over to them on the the 6th of May by MTN and my outstanding balance is R1600. I went to MTN (Rosebank) they advised my balance is R500 and it was a back and forth with MTN and VERICRED. The lady from VERICRED advised that she is confused and does not understand why my account was handed over to them by MTN when payment was already made on the 30th of April. She proceeded to say MTN should refund me so I can make payment arrange with them instead. It has been a back and forth with MTN and I have not received any assistance from them, The representative failed dismally to assist and I am very disappointed in their service I am stuck and have no idea whom I can go to for assistance.