MTN lies in mails, doesn't honor contracts

I upgraded my account on 10 April 2015 at the MTN service centre in Forest Hill mall.<br> <br> From May to July I was NOT billed for my device, despite going in to the same store and two others, and several mails as well as calls to their customer care where I have evidenced screenshots that I held for almost 2 hours, I was told that my billing is correct (I have it in writing on mail and on Facebook) Then in August, I get a mail saying I was right, they didn't bill me for my device. Now they are billing me at a higher rate than what I signed for in store on 10 April 2015, despite me telling them that that is NOT what I signed for and them sending a mail saying it will be escalated to the right department. And because it is done by Debit Order, it went off my account at the HIGHER amount! I have been an MTN customer for more than 15 years, and I am disgusted at this last turn of events.<br> <br> When will this be resolved???? How many hours must I still spend doing MTN's work for them?