Unfair charges on accounts

Hi there I had 2 MTN contracts of which I cancelled one in April . I was told to pay just under R2 047.00, I however rounded off and paid the R2100. Despite this, MTN sent me a bill of R2900 for the number cancelled. I then called in querying this and was told that my account will be credited. They went further and debited my account with R1200.00 and never credited the over charge. Now they still want to recover more money from me with a R1300.00 debit that will go off my account. I have wrote to them on e-mail and used their social media platforms to get assistance. They still plainly ignored me. This is an unfair business practice and if needs be, I will log a complaint with ICASA and any other relevant party that can assist. If they cannot do the job well, then they should consider closing down the company for this pathetic and disgusting service that they provide.