MTN does it again :(

I have been trying to cancel my contract and change to Pay as you Go since I was eligible for an upgrade. No one answers 135. No one is responding to my email to the retentions' department. Once again, as has happened before, my invoice for R1078 is incorrect. I pay R329pm. I never paid or ordered 10 gigs for R468. I've given all my details as requested by retentions but no one is responding. 911 emergency!