horrible service

I am so sad and annoyed as I write this review!!! Supersonic was my ISP for almost 2years and I had no issue with them, but due to rising 'cost of living'', I decided to switch for a cheaper offer. I cancelled my contract in November and they explained that they will still debit me on the 26th Dec, to serve my 30days notice. I agreed and they sent me a cancellation letter. now in January they still debited me!!! I made contact with them via whatsapp and that consultant was so useless, she did not want to listen, took her own time responding and eventually when she finally double checked, saw what i was referring too, but she still insisted that i am liable to pay the invoice for January, how ??? when i cancelled in November already? Im super annoyed because i cant get the new ISP to connect me because they still havent cancelled my contract. this is sooo poor and an inconvenience with the returned debit orders!!!!