Dup Diesel guarantee not honored

I requested Dup Diesel to do a full reckon on my Mercedes injectors, their guarantee of their work is for 12months. My engine seized up after 11months and Dup Diesel refuses to take responsibility for their work. I had the sub-assembly done by a different company and an inspection of the engine after it seized up, it was proven that the injectors was faulty and was the cause of the damage. I took the case to the RMI and Dup Diesel refused to follow their instructions as well.