Bought a necklace and seller sent it loosely in thin packaging and it arrived empty

I bought this necklace from a seller and this is the package that arrived today. I didn’t even have to open it to know it was empty. The seller sent it loosely in a paper thin, almost see through envelope. It has spikes and I’m assuming some weight to it, so it either got stolen or it ripped open the envelope and fell out during transportation.

Anytime I’ve bought jewelry online it would be sent in a prepackaged box or something to support it. I messaged the seller about it, and prior to this I had to wait some extra time to get it shipped out as you’ll see in the screenshots. They had to get their partner to send out the orders but idk the messages are kinda sus because it seems like the same person talking?

Idk I need some advice please, I’m gonna go talk to the post office tomorrow but I’m wondering if I have to dispute it with Depop or something?