If I took my automobile to a mechanic to get repaired & it was agreed upon that I would buy the part myself. The part is installed & but it isn''t work

ing. The mechanic claims that the part must be defective. Is the mechanic still obligated to correct the defect? Long story short the mechanic would fix the problem unless I paid him more money. I then took my vehicle to another mechanic. A frien of one of my brothers. I messed up by paying the money up front. $200.00 dollars. The new mechanic was informed about my situation by myself with the part. I asked him to see if the part was defective and fix it. He claims that he checked the part and it was defective & thus refusing to repair the defective part. He claims that the $200.00 dollars was for him to just & see if the part was bad. Something is wrong with this picture. My question is do I have a claim againsted any of these two mechanics. I also had a water pump installed on my durango by this machanic & it still leaks to this day.