Abused by cell c

I had a contract with cell c for 2years, from 2017 and ended in 2019 December. Then they said it was use in January and February 2020 then I arranged to pay in March 2020 and I asked them to close it. As soon as I realized that they where still charging me even after I closed the account I went to one of their stores and they promised that its closed but they still diducted the amount and I always had to reverse the payment. According to me I don't owe them anything I don't even use cell c anymore, I tryed resolving this metter with them but they don't seem to take me serious this is my last option. Now recently they took R500 and its irreversible Im tired of cell c. I'm a single parent i can't afford such an inconvenience