Debiting account even after contract closed

Last year October my contract expired with Telkom Mobile. Sent cancellation form to them in November and heard nothing, followed up in December still nothing, followed up in January still nothing, followed up in February and was told to please complete cancellation form, resent email from November with cancellation form heard nothing. Eventually mid March got feedback that account has been closed and apologies for the inconvenience. End of March debit order on my account so I had that reversed as the account does not exist anymore. First week April another debit on my account with a different reference number from Telkom Mobile which I also had reversed and now 16th April another debit order which i have also reversed this morning again. Don't know how long this is going to go on with but it costs me R50 every time I have the debit reversed. Can someone please tell me who I need to speak to to get this resolved once and for all and I am getting really frustrated with the excellent service hence the reason I moved back to Vodacom in the first place. In the interim I will continue to reverse every debit order done on my account until this stops.<br>