6 Month no refund

Purchased a set of hubcaps 13" INV 11G90354(01/03/2017) from Margate branch . Put the caps on the wheel and they cracked. Took the product back, Duresh from Midas removed them and they cracked further. Salesman Duresh would organise a refund so we purchased a set of Midas hubcaps as the refund would take a few days. I installed the hubcaps with no problems. Went back to Midas Margate in April (a full month later), was informed that head office had not passed the credit yet. Went back to Midas Margate in June, still no joy. Its terrible dealing with suppliers who do not know what to do and have no power to make a decision. It is now September 2017 and still no refund. Do Midas not guarantee the goods they sell, they are my supplier so why do they not honour a refund ?