Complain

I bought ploughs for my car,only to find out I bought the wrong thing.paid cash for that and when I tried to return them the same day with a slip I was told that there's no refund.No big board on the till to show that there's no refund.they have no customer service,even after I showed them my slip from my last purchase which was last month to show that Iam a regular/customer they still couldn't refund me.