Supersonic Fibre router, Black Friday special

I bought a router which was on special on the 30th November 2020, which was delivered on Tuesday 1 December. The router failed to work and I was told the Sim card could be damaged. Another one was delivered on the 14 December and it still didn't work. On the phone the Sim shows that it's registered but somehow when inserted into the router it doesn't work.

My husband and I have tried without luck to get this resolved. We've been sent from activations to their technical support, with one of the agents even telling us that she had escalated the case to her manager. The frustrating thing about all of this is that no one ever comes back to us. We always need to call in and spend our airtime on hold with people who can't assist.

I received my invoice this week which they obviously expect me to pay, but I haven't had any joy for the past month. Is this fair though?

Please assist