Mtn refusing to cancel my wife's contract

My wife Mrs MA Moeketsi registered a query on MTN website with *** on 14-10-2015 @ 18:21:32 to have her contract converted to prepaid on expiry (18-11-2015). She even took the screen capture as proof. We were surprised when Mtn loaded bundles again on 14-12-2015. I called the call centre on 18-12-2015 to investigate and spoke to Given Lufuno Matidza. He informed me that my wife should have called on the 19-11-2015 to cancel the contract and the fact that she logged the query on the MTN website and has a ref number to proof this does not count. What i find astonishing is the fact that this is part of the service that is offered on the MTN website. The other concerning fact is that when I asked him to check the ref number on the system, it came out with a different time and query. The query he gave under the same ref number was logged at 17:48 and is completely different to what we requested. We would like to have the contract cancelled with immediate effect and the bundles reversed.