[mothered]

What should I expect when the three days of the investigation are up? Will they just give me the refund because the weight of the product is so low? Or will they make me file a PR?

It's not possible to determine the outcome of their Investigation. At the worst-case scenario, they'll liaise with the manufacturer.

They're currently checking the consignment against the carrier's records, so wait for their reply and (If need be) we'll tackle It from there.