Shocking service not taking responsibility for shoddy work

I have had my truck repairs done at Sprinter Zone. Clutch and pressure plate replaced. 20000 km later total clutch failure. Blamed my driver and overloading. I had to pay for another clutch . 4000 km clutch failed again. Blamed overloading which was not the case have all loading sheets as proof. Found out later each time they fitted poor quality parts after i had been charged for another clutch. My opinion is they keep installing sub standard parts to increase revenue and income. Dont use them .