Refund Refuse

Bought a spare part for an oven. I was told that it is the correct part I was looking for and the salesman assured me that it will work. The said part doesn't fit into the oven so it cannot be used. Upon trying to return the part for a refund, they told me it's not their problem and refuses to give me a refund. The salesman was very rude and condescending. Even though the part is unused and in the same condition that I bought it in. They were very eager to sell the part but won't assist in a reasonable solution.