Cancellation

Hi Hope you are well I have been trying to cancel one of my MTN contract accounts BA*** ***). I call retentions many times, they have me a settlement amount of which i paid at the MTN store in Irene mall, i then called retention to cancell the contract . i did this 3-5 times. The last time i did it i asked the store manager godfrey to assist me. Retentions have me a settlement amount, i paid if and i called retention to cancel the contract. The store manager was with me, he confirmed that the contract will be cancelled. Now when i try to upgrade my contract on my current number *** i cannot. MTN says that i owe money on the contract after i settled it because the contract was not cancelled. Please can you assist. Thank you Timothy