MTN is ignoring my letters of complaints

I've so far sent two letters (April 2014 & April 2015) of complaint to MTN about overcharging my account. I was charged R5600 in April 2014 and R7750 in April 2015 and there's not justification to these charges. My monthly average spent on my phone is R2200pm so I was amazed when I see this discrepancies. I then requested for MTN to account for these charges and they've never even bothered responding to me. I'm really very upset about this and I have asked for an itemised billing on my data charges because everything is accounted for as packet switched data calls, but what are these data calls if they can't be accounted for? Surely we should receive an itemised billing on data like we do on voice...these operators should tell us what they say we spend our megabytes on, they should also be transparent in their pricing of these megabytes. I want to write to the DTPS, ICASA and NCC to request them to mandate these on them. Surely this is day light ******* if people can just charge you as they please and refuse to account for these charges. It's frustrating to feel this helpless but I won't let this to just go away.