Contract cancelled but money still being deducted

I had an account with Cell C , on the 25th of February 2015 i settled ( R 1983.48) and cancelled the account .But they are still deducting.Money deducted from my bank account March 2015 (R1747.27),April (R3150.63) and May (R3070.64), I went to Cell C to complain several times and they told me everything is sorted , but the money is still being deducted. i am not happy with service at all, as every month i have to go to Cell C for the same thing and i dont know what to do anymore PLEASE HELP.