Cell c deducting money

Cell c has been deducting R288 from my account since March 2019. The account was paid and I have proof. Have contacted them numerous times asking what this amount is but no one can answer me. I cancelled the contract paying in full what I owed, which should have stopped end August. They are still deducting money. Claiming it is for services being provided but not paid for yet. So why when the contract was still active did they start deducting the additional money already? And this amount being deducted do not appear on any of the monthly statements that they send. I do not understand how no operator can tell me what this money is for and why it does not appear on the statement?????