They have been billing me for the past for a cancelled contract

I cancelled my contract 3 times with Telkom and they have been billing me for 4 months for the same cancelled contract. I am about to block them from my account even though I have another contract running with them. I have even filled in a cancellation form spoken to managers. They have even cancelled the service but they are still billing me. i just want them to stop billing me and refund my money