Selling faulty car parts!

I recently purchased a fan switch from Goldwagen for my Golf. The fan switch came from a company called Worldwide Automotive Group (WAG). It did not work so I explored other options and payed a mechanic to diagnose the problem when I could not find the problem myself. He told me it was the fan switch. I told him it cannot be as I have just put in a new one. He told me to buy another one. I then had to spend more money taking time off work, putting petrol in and driving to purchase yet another fan switche which surprise-surprise also did not work! (The second switch also came from the company WAG)

I then had to pay yet another mechanic to diagnose the problem and he too said it was the fan switch! Only this third time I asked for a different brand of fan switch and guess what, it worked!

I want my money back for having to drive to Goldwagen more than once to buy a fan switch, I want compensation for having to take time off work to go more than once to buy this switch, I want my money back for having to pay mechanics when I already knew what the problem was, I want my money back for the two faulty switches and I want the money to fix my cars engine that was damaged from me using your switches which did not work and allowed my car to repeatedly overheat.

I asked Goldwagen for help and they sent the switches to WAG for testing and WAG decided that they do in fact work. I emailed WAG and they admitted to me over email that they DID NOT test the switches in an actual vehicle. I requested they come here to my house and test them in my car so they can see that they do NOT work before they decide to officially NOT compensate me. I received NO reply for this request.

They are refusing to refund me or pay my expenses caused by them and they have nt returned my switches after testing them so essentially this is now theft as I am not in possession of the switches that I have paid for.