What should I do to sue a store that sold a defective item and refused to issue a receipt as well as the change?

Is there anything I can do when I purchased a point scale from a store and cashier is refusing make things right? Scale was only 25$ and I handed cashier 30$. He closed the drawer and denied a receipt. I went out to the car to check if scale worked I weighed out with exact weights to find a far off reading the scale was defective. With no receipt, it voids the warranty. They won't even exchange. In fact they started getting hostile towards me even though I was holding my 4 year old daughter.