Audi sandton sold me a faulty part and cannot refund me

i bought a PCV valve on Friday 25 October 2019, took my car for repairs at Humpkuli Auto in Midrand, after fitting the new part they realized that it was faulty and called me to come collect my vehicle. i took the PCV valve back to Audi Sandton and explain to them that the part was found to be faulty, the guy by the name of Wilson told me that he cannot process for my refund because his Manager was not at work and told me to call him on Tuesday when his manager is back. i called and they told me to come through, when i got there i was told that in order for them to refund me i must give them a confirmation in black and white that shows that the part was tested and found to be faulty from Humpkuli Auto, i drove back and got that confirmation but they could not take it and requested me to go and get it tested at VW, i was angry for being sent from pillar to post but finally agreed. they told me that i wont pay anything at VW and i booked my vehicle at VW Centurion, when i got there i was told that i need to pay R1100 in order for them to do the diagnosis on the part. i called Audi Sandton and explained to them but they told me to leave, they are busy playing hide and seek games, they wasting my time and fuel. these people are very unprofessional i even regret for buying from them.all i want is my money i even bought anther PVC valve from other dealers. I WANT MY MONEY BACK or i am gonna take this further.