Contract cancelled but still deduct money

Two months ago I cancelled my contract with Virgin Mobile. But still they deduct R172.00 VMSA*A******* from my bank account. I have phoned them the first time and they promise to pay back which they did not. I have phoned them again and they promise it will not happened again but for no reason suddenly they cannot give my money back. Now this month again they deduct R172.00 from my account. The service with Virgin Mobile is up to ****. I do not know if their is any body that know what they are doing their.