Data theft

I have a 20GB Wifi month to month contract with Telkom. Over the weekend my GBs ran out and so I purchased 10 more GBs. I however at the same time have decided to move to a cheaper service provider and logged to cancel my contract. Today Portia contacted me to assist with my cancellation but tells me that the 10GB that I purchased separate to my standard contract will be forfeited and the charges for it will not be reversed. In essence this is theft. I am paying extra for a service on top of my standard contract and I should therefore receive the data that I have paid for or the charges should be reversed. To add I have only used 1 GB of this data. I am now so happy that I am moving away from Telkom and will never return.