Contract agreed to not capped in error

When I renewed my top-up contracts with MTN the agent recommended switching to a normal contract. When I expressed my concern about the potential over billing on these contracts which I have experience in the past, she advised that the contracts can be capped so that you cannot exceed the contract amounts. I agreed to this and the contracts were concluded with capping. So you can imagine my surprise when I received a R631.45 bill for a R289 contract, followed by a R1,661.74 bill. When I queried it with MTN I was advised that there was a system error on the capping & that the amounts will be credited. No credits have ever been received and I have reversed the debit order, paying contract amount as agreed to. But like a good customer I went back to MTN to sort it out to discover that the account had still not been capped, and it was presumably done again for the umpteenth time now. I have emailed customer care four times and been into the store twice to get it sorted out and have had no response or service from MTN. I am about to cancel all four of my contracts and I will see them in court before I pay a cent over the agreed contract amount. They owe me credits of R2,625.60.