Horrible Service

I signed up for a sim only contract with MTN(mondo) for R199 per month for 40Gigs(20G pick and 20 Gig off Peak) however I got the bill from MTN for R300. I called MTN and they advised that my contract if for R300. Logged an investigation with them last week Friday, still no feedback and when I call their call centre they don't have any feedback . The last lady that I spoke to advised that the person responsible for my query is unavailable and there is no 1 else that can assist. Kindly rather process a cancellation for the contract