EditaD

our company (UK based) manufactured product and sold to Italy. 6 pieces with a value of £550 per piece. incoterm EXW, courier FEDEX, using customer's account. Appon receipt in Italy, customer noticed that they received 4pcs only. We have to send them missing quantity. How properly do export on shortage? Should we credit invoice for customer for the 2 missing pieces and re-invoice them with shortage shipment? Or can we just send 2 pieces with invoice, which would have no commercial value (commercial value would be for customs clearance only)? Will customer have to pay duties on both shipments?