A repair without an SLA

My backup was installed last year, law and behold the first inverter kept on tripping, then Paul installed a refurbished inverter that tripped on the spot. A year later and the inverter stops working. It was sent for repairs last week but he didn’t even acknowledge receipt of it, there is no SLA to advise when it will be returned yet he has the nerve to ask me who am I employed by. His arrogance and lack of customer service will lead to another failed small business.