Bad back up service from Builders Warehouse re : Gentech Inverter

I purchased a Gentech Inverter Trolley 1600W HYBMSW on 14/09/22. I installed the inverter early December by a qualified electrician. Worked well for about two months and than started slowing down. Removed inverter in March 23 and returned back to Builders Warehouse Centurion. I was called back in two weeks notifying me that the supplier not willing to repair or refund. I need to purchase new batteries. I refused to accept this and asked the consultant to go back to her manager and supplier. Also to give me proof that there was only three months warranty on the product. Still waiting. I am disappointed in Builders Warehouse as they are reputable and should be backing the products they sell. If the products are inferior they should not be supporting the supplier of these products. I would like Builders to refund my money and deal with the supplier. I purchased from Builders and not from the supplier. Builders need to at least honor a decent guarantee. To the public please do not purchase this Gentech inverter. An absolute waste of money.