Contract cancelled - but still being billed

I have two contracts with MTN, one for my handset, and one for a data deal.

The data deal contract reached its 24 month term in September last year. I called the call centre early last month to cancel the data contract, the lady had confirmed this to me over the phone, and said that the contract as well as the number had been disabled. I confirmed this my trying to call that number, and indeed, the number has been cancelled.

She gave me the following cancellation reference number: 262 135 545

However, I am still being billed for this contract.

This is obviously frustrating, Please rectify or update your system.

I am also due a refund for this last billing cycle (on the data contract), as the contract had already been cancelled.

Thank you.