Payment for service

This is my second time complaining about Vodacom. My mother is a Vodacom customer for years. She cancelled her data contract with Vodacom before the cancellation due date. The contract was cancelled, but still, they are deducting payments from her account, now for 6 months. We have phoned and emailed several times. In the beginning, she had someone phone her and promised the problem would be sorted, but now they are not even phoning back anymore. She has so many reference numbers and pages of emails send, but still nothing. Every month payment is deducted from her account. This is lousy