I would say don't bother. Don't cry over spilt milk. Just an extra $40. But, if what you had posted is not a one-sided story, i would definitely claim a refund for the missing items, let alone give then an extra $40. If they refuse, i would make them unload the stuff back to my house. $250 is the average price for hbd flats, but if you are living in condos, bungalow.etc they tend to mark up their price. Once they reach and see your stuff, they usually will complain how difficult your stuff are to transport.etc so its expected. But once they give you a price, dont let them increase the price. You can easily get someone else to do it even if you have to wait a day or so.
