Poor customer service

Good day, I went into taxi city spares in Richard's Bay recently had my sample of what I required the sales person sold me the wrong item/part went back within 24hours and the owner of the bussiness said return on Monday he will order the right item I did so go there expecting to receive my new part the gentlemen says to sorry but the sales person that sold the wrong item to me resigned and that he cannot exchange nor refund me he then tells me to buy a new part which cost R600 yet I already but that amount for the wrong item I wanted to threw my toys out my court but he said he will charge me for assultant and languages used against him, please citzen out there please help me resolve this matter or whom can I speak to get my refund back I am unemployed and have a family to support as well.