Refusal to refund and incorrect part supp****

I bought a tow bar plug housing with Vin number. I was given a wrong part as it did not have a bracket to accommodate wiring fitting. I made it clear what I wanted and was given wrong part. Agent should have offered me correct part given that he had my Vin number. Now they refusing to refund me. This bis so ********* as the part has never been used. I can't use it either is its current form as it is incomplete. I bought my Amarok from them and I will never give them business