Pfandfrage on inappropriate spare parts

Hello, at Autodirekt bought a hydraulic pump for my vehicle. According to the website this pump should fit (car, model, engine and year of construction all correctly entered). For this payment about 90 Euro plus 90 Euro deposit about. Now the part did not fit and I had to buy another hydraulic pump. Now I wanted to return the unused new part, but was unfortunately already over the 14 days right of return, when my mechanic and I realized that it did not fit. e declined because over the 14 days over, Kulanz rejected, because the part is bought too little. Now I wanted to have the deposit for a hydraulic pump back. That was rejected. Without return of an old part, there is no deposit back. I wanted to ask now if this is so correct, or if they are actually obliged to admit to me the deposit back, if they send me a wrong part and don’t want to take it back any more.