Telkom contract expired but telkom keeps billing

II took a Flex on 2 deal with Telkom and I have never skipped a debit order. The contract came to an end, one of the numbers have been successfully cancelled and no further billing is taking place. But with the other number, Telkom keeps on billing me and I have went to Telkom store to cancel the number for me and they keep telling me that no further billing will take place. It has been 3 or 4 months I have been trying to cancel the number but nothing is happening, instead the bill is not coming down. I have been trying to call Telkom to try and speak to their agent but it is quite a mission to get through their agents.