[Checkpoint]

Hello, today I received a product worth 200 euros from an international company.
It's quite hefty: 3 kg.
The tracking service they linked me, which covered the first part of the shipping, correctly displayed 3kg of weight.
BUT the second part of the tracking (the one that followed the journey in my country) displayed an erroneus weight of 0,1 kg.

So I thought of trying empty box, since I have the "evidence" of 0,1kg displayed on the second tracking site. I emailed them and they asked photos of the package and of the shipping labels attached on the package.
Now what should I say? that the package itself was empty (suggesting that something happened during the journey here, and I think they will blame the carrier) or that the product box was empty (suggesting that there was a problem in their warehouse?).
The problem is they didn't send a box, it's just a plastic wrap package, albeit opaque so you can't see inside. It's quite light an flexible so it would be a bit incredible that it was completely empty. Sadly they didn't send a rigid cardboard box to carry the product.

If I said that the product box was empty, it would be a bit more plausible, but they could counter my statement saying that they have CCTVs in their warehous and that they can confirm they picked up the full product and that basically it's not their problem.
If I said the shipping package was empty, they will launch an investigation (as they told me in the email). I'm a bit scared they would blame the courier of my city, and since it was absolutely clear that THERE WAS something in the package, he would come angry at my door knowing that he's basically being scammed. Although it would be quite difficult for him to remember the exact item and address I guess.

I wonder what would be the best course of action in this case.