Horrible service

I bought a Mercedes petrol at VSM Spares in Edenvale and I asked them if I can bring it back if it was not right and l called them the same day to notify them about the part being wrong and I was told to bring it back on Monday. Which my husband did and we were told to bring the sample to the part and again we came back after stripping the part from my car now they telling me they will give me half of the money and the rest later. I paid 5500 for the part now they want to give me 2500. After all I trouble l had with them how do I trust if I will get my balance