Unauthorized debit orders

I'm really frustrated with cell c and I will be taking this matter further, my contract will the company ended in December 2025 and I have paid the full amount, End of January cell c attempted to take R70 from my account without my knowledge and I acquired interest fees of R115-00 which I had to pay to the bank because it was an unpaid debit order, I called cellc spoke to a very rude lady and I paid the R70-00 immediately, now all of a sudden end of March cellc attempted to debit R70 again and I'm now owing the bank R115 again without my knowledge and I was told that the previous R70 was the last one, am I going to pay cellc for the rest of my life just because I once had a contract with you which ended months ago? How do you get into my bank account without my knowledge and on any random day ,that is *****.