Billed for cancelled router

Requested for a downgrade from previous plan I had to Rain one 3rd July I got my new router and I also requested for the previous router to be cancelled agent advised it's cancelled and I won't be billed till they collect the router as they use couriers to collect the routers I waited till the 22nd of July that's when they collected the router Now checking my invoice for August I see they billed me for the same router I requested to be cancelled. Called the call centre and I told them what transpired the agents just tell me they are checking what happened and they put me on hold till they hang up still haven't received any help as this is still left hanging. Not happy with their service as they are not transparent to the client. This is still not resolved now am billed R941 for 2 routers which one is supposed to be cancelled.