Contract cancellation

I called to cancel my contracts two years ago. They cancelled the phone and leave the data contract. been calling almost every month to see why it was not cancelled but nothing is been done. We so not use the data. Now i get threatening blacklist letters because the money is accumulating. Please tell me why one contract can be cancelled and one left out. I requested for both to be cancelled same time. I have been to various mtn stores but consultant can not help me as they say cancellation is done only on the phone.