WebAfrica unauthorized debit

I joined WebAfrica in March 2017 and ordered a router as part of the package. When I was told that the router will take more than 5 working days to deliver I decided to cancel the router. I then went to electronics store and bought a router. In 2020 around June I requested an upgrade on the internet speed and this was approved. A few days later I checked my internet speed and it was still not yet upgraded. I logged onto my WebAfrica for the first time in a very long time and that's when I noticed and active invoice of the router I canceled in 2017. I then contacted WebAfrica to remove the invoice and do a follow up on the speed upgrade. WebAfrica then decided that in order to clear the invoice, they will have to debit that money, which they did. I immediately contacted them and requested that they investigate the matter. The lady told me that I skipped 3 payments in 2017 when I joined them in Jan, Feb and March. This is not true. Besides, my monthly debit order was just under 400. 400 by 3 will never amount to 899 which was the price of the router reflected on the invoice. I then decided to cancel their services since they don't know what customer satisfaction is. Now they are constantly debiting my account and I keep reversing it and every month the debit amount goes higher.