Supersonic is not serious

Good Day

I signed up for internet with Supersonic, my router was delivered first and a few days later I received my Sim card. Upon receiving my sim card I inserted it into the router but the router isn't work, I know this because I tried with my old router and it worked perfectly fine. In fact I am still using my old router up even now. I called several times and I was told to do troubleshooting so many times and it still doesn't work. It is a ZTE 5G MC801A Router. I called back again on the 20th, the lady told me that she will give me feedback and I am still waiting for any response. So I would like a replacement router please because this one I have doesn't work.