Mondo and MTN made misleading offer to me.

I was contacted by an agent from Mondo offering me benefits on my MTN contracts at no extra cost. I repeatedly asked the agent if I will be made to pay anything extra and the agent assured me that I am going to pay the same amount they are just giving me extra benefits as a reward. When an invoice came after the 17th I realised that, I was **** to again. The invoice came with an extra R1600 that I didn't agree to and also didn't budget for. I called MTN which referred me to Mondo which was surprising because I have contracts with MTN and my contracts were altered by them, and they gave my information to Mondo to lie to and make false and misleading offers to me. Mondo did an investigation and agreed I was **** to and will initiate a reversal of those benefits but I still have to pay the R1600. A week has passed and my contracts are still the same. Each time I call Mondo they tell me they sent information to MTN to reverse, but nothing was done even now. MTN is using Mondo to mislead clients who are paying well in to increasing their benefits and cost to increase their own revenue.