They refuse to give me my refund back,Very Poor customer service

I bought brake pads yesterday 15:24, when I got home took it to my mechanic and he said the brand won’t give enough mileage and is a hard one. Because I use the car daily and I just need it to be sorted out, I told my mechanic that it’s fine I would just take back the product to Midas he can buy me the one he prefers. When I got to Midas today 08:45 I got a shock of my life they refused to refund me my money back.the brakes were still sealed as they gave them to me and I had an invoice. Told them I need the money back, times are really hard i cannot afford to take a voucher I need my money back. Phoned their head office stood there for hours trying to get assistance. I will never shop there ever again. And I will tell all my close family friends and fam too.