Still charging me 4months after I gave notice

I had a LTE contract with Telkom. I gave the appropriate notice to terminate it since I now have fibre. Despite following the necessary procedures I am still getting invoices and Direct Debits are being processed. I first gave Notice on 30 October 2017 and have followed up with the call centre several times and even visited the V&A shop. Customer service at first told us it was being processed and that it usually takes a couple of weeks and they would refund the charges for the services not being used. And this week I get another invoice. It is impossible to talk to anyone who can tell me whats going on. Each phone consultant tells me it will be rectified and the account has been cancelled although I still get billed!