If Contract is cancelled, why debit?

So, I took up a mifi router with Telkom via their sales department:10213 on the 10/10/18. Product was delivered but I then decided against the product without having used it. Their returns policy states that a product can be returned within 7 days, so I exercised that right. I thought that our business was done as the courier company collected the item. To my surprise, my account was then debited the following month and it has been debited every month since then. I had queried this with the client care team but it got nowhere. I've had different case numbers( ********** 5, ********** 5, ********** 5) opened then closed and reopened again without feedback. It got to a point where I reversed the deduction but this didn't solve the issue. Long story short, I contacted the sales team today, who informed that the account: ********** 37A is not active. So why am I still being charged?