Big No Go For MASTERPARTS

Big No Go for Masterparts,I recently bought a fuel pump for a bmw e90 , got it fitted but the fuel gague gives incorrect fuel Reading, When I fuel up instead of the gague moving up it shows no fuel in the car ,very scary and difficult to use . Sent it back to them for a claim they advised the technicians will check the part , this process took over a month and only to come back and say they part is fine my car is the problem, I'm trying to explain to them I bought a new pump from Goldwagen and everything is working fine , I offered to take the car to them so they can do what Ever test they want on the car instead of blaiming the car , not happy with their service and very disappointing they assuming and making statements that are not true also they not responding to me now .