Bad customer service

I was offered a Vodacom S90 Plus 4G FWA home internet, when I received it had connection problems. I called them and they logged a call and the back office came to me and informed me that there's no network coverage in my area he advised that I returned. I have returned the router and cancelled the contract and I've received an SMS that the cancellation is not confirmed yet till now. When I look at the App they have charged me for this router even though I have returned it and cancelling the contract. I've sent a follow up email requesting some clarity on the cancellation and this amount I apparently owe them, I have no response from them. They have also blocked my calls. It is really frustrating dealing with Vodacom online.