Won't cancel my subscription

I took out a six month ADSL contract with MWeb at the end of September. I was told I had a five day cool off period. I tried to cancel it the next day before they couriered my router. The salesman I spoke to told me to speak to accounts. I tried twice. The first time I was on hold too long, the second time the call was dropped during transfer to the retention department. I logged the request to cancel through their web chat and got a reference number. The next day, the router was delivered but I sent it back with the courier. Since then, someone from MWeb has contacted me to confirm my cancellation. Today, two weeks later, I received a sales agreement for the router I don't have to say that if I don't use it within 60 days, they'll charge me R799 for it. This is ridiculous!