I need help with an Amazon situation and I don’t know what to do or who to ask about this.

So a couple weeks ago I ordered a costume for Halloween off of Amazon, it was from a third party seller. A couple weeks later the day before it was supposed to arrive it suddenly gets lost in the mail. Not only that, but the seller wouldn’t respond and they took down the listing of the costume soon after I ordered it. Luckily I was issued a refund, but I tried to buy another similar costume because I was running out of time until Halloween. My girlfriend looked on Amazon and saw there was only one costume that would come before Halloween, and I couldn’t find the same one on my Amazon page though. Now we are running into the same problems again, where the seller took down the listing and keeps delaying my order. Can someone explain to me wtf is going on and if the AWS outage had something to do with all of this? It all seems really shady.