Unauthorized debit

Received home router bought online 18 September 2025, Canceled contract 02 October. The contract cancelation due to unavailable network 5G, hence consultant confirm during purchase that it's available in my area.

My problem is that I have been paying from 25 October debit check of R666 and 25 November payment of R870.01. I have received the Messages that 20 December debit will be done. Need assistance for this cancelation. At some stage of my complain, I was advice to reverse this debit but unfortunately unable because it's a debit check.