Poor service and attitude from Mecer

I bought two 3 kW inverters through a company called Carrera Solar on the 4th July 2022. They were installed by a qualified electrician on Thursday the 7th July. One of them worked perfectly and the other was faulty from the outset. I contacted the supplier who collected the faulty inverter on Friday morning the 8th and promised to return it the same day. I am still waiting for them to sort out the problem. The feedback I have got is trying to blame the installer who has installed 5 inverters for me with no problems. I hardly think that is the problem.