Disappointed on builders warehouse.I always believed in their quality product

I bought ARISTON instant water heater.It never came on ,when I told them they send a plumber ,still it did and the plumber took it away and came back and said he tested the unity if fine...then I took it back to the store cause I wanted my money back since it was not working in my house.They said I can not get my money back they will test it again and see if there is any Fault they can only replace it

I went back to collect it the lady at the front desk said it never left the store,so I must wait while she was helping someone on the phone. While I was still waiting another lady approached me and ask if she can help me I talked her I was waiting for the other lady, and then she said oh it about that instant heater ,it came back yesterday and it was tested nothing wrong with it.Shecsaud I need to put 40m curcuit breaker....I told my electrician we change it but now it tripping the power. I'm really not happy,I feel they sold me something that had fault but they don't want to admit it.