Vodacom has bad service

Good day

I had a contract with vodacom, which ended 2019 December but then to my surprise on January they debited again. On February I called them to cancel the contract but then the lady was busy prompting deals on vodacom and I told her that I called in terms of cancelation but then she said she will call me back on Monday but then she never called me back. Month end February they debited again and i reversed the money later March I got a message that I am owing and I tried calling again but I was taken back and forth with no resolution. What I don't get is how do they keep on debiting even when my contract is due and after I am the one who is owing them.I mean they know when my contract is coming to an end and they should be contacting me to let know and whether I want to carrying on or what... But it seems like they take that decision for me.