Telkom refuses to cancel services and stop billing long after a number is ported

I decided to port my number from Telkom to a VoIP service provider because Telkom refuses to review their land line rental prices. I phoned in to enquire about the process, I was told that I must NOT give notice to cancel the service 30 days before I port for 2 reasons 1 because if i do the number will be canceled and lost, there will be no way for the number to be reallocated to me. 2 because the port will not take place if there is an Order on the system. I initialized the port through the new service provider and after a few attempts and Telkom trying to derail the port it went through. The following day straight after the port I sent through my cancellation letter dated 28 March 2018. I then followed up telephonicly a few days later. To cut a long story short I have resent the same cancellation notice to 3 different managers twice a month since the 28/03/2018 and followed up by phone a few times and Telkom still continues to bill me 30 days in advance every month for services they are not providing. Thank goodness I don't believe in debit orders otherwise they would be debiting my account. On the other hand If they did I would may be have a better chance of laying a charge of ***** and theft against them. When I contact them they say I must pay the account in full, then they will close out all the services on the account, credit all the invoices and refund me, but they are billing for services in advance which I have ask to be canceled regardless of or if there are amounts outstanding on the account. Don't forget Telkom themselves cut off the line so the port could take place, hence the account was up to date at the time of Porting. So once again, is that not some kind of ***** where you are invoicing for services not rendered in hope that the invoice slips through and might be paid by an uninformed accounts department. Imagine the profit from taking R300,00 a month from 100's of companies who's accounts departments are totally ******** to the fact that the line has been canceled many years ago. Very few accounts departments will actually query a Telkom bill, it just gets paid because it's one of the many phone lines the company has.