Bad Servise

I went to Midas Roodepoort on sunday morning and buy a cam Belt for my car and gave them car description and all that but the guy who was working there gave me incorrect part, so by the time my Mechanic saw that its an incorrect part we went back to exchange but they were closed already because its sunday they close early. so we decided to go and buy elsewhere and we got the correct part. so this morning i went to midas with incorrect part and now they are telling me that they cannot refund but according tio their Slip THE ONLY NON-REFUNDABLE ARE ELECTRICAL PARTS AND DAMAGE GOODS. for me its very bad service and even a Supervisor Lady came and before she can even want to listen to what happen she just jumped into conclusion. but i dont see myself and my Family buying there again