Mecer and boulders warehouse useless

Bought a invertor from builders warehouse in Feb 2023 unit went faulty 3 months later they send it for repairs took 21days came Back full of scratches and had a different fault now I contacted builders that asked me to take pics and email it to them then told me to return the unit to the store for repairs again which will take 21days I gave the unit in I'm kit happy I want a new unit or a refund which they refusing