Disloyal and de*****ing people

I tried talking to their WhatsApp number to try fix my line as I was working from home and I did not have network connection and after so many back and forth without them being able to fix the problem I then decide to cancel and get something else to keep me connected for my work. They told me I owe them and then after I return the router the money for the router will be minused, I gave them the router and still they charging me for it. And also there was nothing about cancellation fee on their advert it said hassle free cancellation and prepaid so if you don’t pay you dont have services, so they selling lies to people. Today they handed me over after collecting their router and not servicing me well.

Can I get assistance please on this where can I report this.