Incorrect Product: Refund Request

I went to buy a Throttle Body which I gave a sales consultant an engine number so I can get the correct item unfortunately it was not correct when it was supposed to be fitted to the car by mechanic.

I have been communicating with the sales consultant who tried and get a correct part but unfortunately I cannot afford a new price then opted for a refund which I am being informed that they are to charge me 20% handling fee.