Contract Cancellation

I have been trying to cancel a mobile contract since November 2017 with Telkom. There stores cant do the cancellations so you have to do it online, however the process never gets completed and their error message states that someone will contact me. I have placed a debit order block on my account for telkom related paymenst. They can see from their records that i havent made use of the service for more than 12 months, i have blocked their debit orders, but still they try and debit my account.