Fautly product not replaced resulting in long delays

I bought an inverter, and the thing blew up after using it for only 1 hour. It charged my blue nova lithium battery on the 20A setting for that duration, and had 2 WiFi routers connected to it - hardly a big load for the 700W it is rated for. I'm being refused a replacement and have to wait for a lengthy inspection and repair process. I sat last night without power for 6 hours, exactly the situation I wanted to avoid. It is unacceptable to me that I have to suffer because I was sold a faulty product. Any shop worth their salt would have swapped it out for me on the spot.