Overcharge on monthly subscription fees

I have upgraded my account to a MTN Unlimited Sky package at the end of December 2014. The upgrade contract was signed for the sky contract at R1299 per month due to the fact that I did not take a new handset. I am however charged for a handset as well as a higher monthly subscription charge. I am charged at R1500 for Feb 2015 and R1700 for Jan 2015. I have spent numerous phone calls to the MTN store in Menlyn where I have done my upgrade to resolve the billing error. It is at a point where they cannot assist me and asked me to personally resolve this with the service centre. This matter has been outstanding for the past 2,5 weeks. I have phoned the service centre several times just to end up being quit on the call by MTN - apparent system failure? I have signed a contract for an unlimited package of R1299 per month inclusive of VAT per month and I want my bill to be amended by MTN so that I am only charged R1299 per month. I think it is unacceptable to spend hours on the phone not being able to resolve such an elementary issue.