MTN Corporate billing blunder

An MTN corporate sales agent offered me a contract which was linked to a corporate discount based on the account of my employer. I accepted one of the quotes presented to me by the agent. At the end of the first month I was billed and the bill was higher than the quote I had taken but I assumed that some prorata had been built into the bill and expected to be billed the quoted amount the following month as I had taken up a top up contract. The bill which arrived the following month was for the same amount as the previous month and upon enquiring with MTN soon discovered that the corporate discount had never been app**** as per quote on my contract. I've called 808, 809, MTN corporate and visited my internal MTN branch office to have the issue resolved. MTN has also not been willing to provide me with the recording for contract uptake. MTN continues to bill me an amount I did not sign up for and have not shown an willingness or urgency to resolve my issue. When I asked them to terminate the contract i was threatened will penalty fees even though it was MTN who had sold me a contract under false pretense.