Service deliver - rudeness and disrespect

I have never been so disrespected and undermined like the way this branch service manager did. I took my tuned 330d for oil change but rather than just servicing my car they went over and above to perform some scans/diagnosis which in turn messed with my transmission. My car came back jerking and not performing nor changing gears properly, went back to find out why and the manager told me straight that he will not take any responsibility for that not to even check what's wrong depicting that they can't check modified vehicles yet they diagnose and service them. Take your car there at your own risk.