Bad service

I ordered a windshield for my C-class and paid upfront. I came they fitted it and problems started. It has oil and when it is raining I can't see the road, rain sensors no longer working. I told them and they ordered from the same supplier and had to drive again 115km to Empangeni so they can fit it. When I arrived the same poor quality windshield and had to go back and was told I must come back again they will order somewhere. Where do I get money for this up and down as it is not my own doing