Upgrade for R368 Billed R1777 cause store failed

I have been on MTN for 2 years and in March I upgraded to LG G3 R368 Top-Up Contract. The store failed to activate my limit as they claimed the system failed. I was billed R1777 and I contacted the store who advise me to pay my contract fee and top-up fee, which I did. The next month MTN billed me R548 plus outstanding amount of R1300. I only paid my contract fee of R368. As I have been in contact with the store for more that 8 times complaining and asking them to just cancel my contract as they have done a bad service together with MTN. On ITC I am currently in arrears for R1400 and MTN has cancelled my outgoing services and no one is willing to help me as this was never my fault. please help me.