Being billed for a product that I rejected. I***-0

Late last year, I took out a Vodacom sim only contract I***-0 but I was advised by a Vodacom representative that the sim deal will only work with a Vodacom router. Afterwards when the router was delivered, I rejected the order. I thought that the contract will be automatically cancelled because my package was returned but a few days ago I received a email that I am being billed for a product that I didn't use including to cancel the product I need to pay a cancellation fee that I was not informed about. I am disappointed in Vodacom, I'll never take their products again.