Unauthorized Purchase

Is there some sort of scam where an unauthorized purchase is made on reverb and sent to you? I’m building a partscaster and have parts coming from Warmoth, reverb, a music store in the north east and stratosphere. My order from reverb was around $100 but I got another charge from them a few days later for around $500, no indication of the order in my account and no emails from reverb about it. Everything on the $100 order is as expected. CC says I have to let the charge post before I can dispute it. I already have everything I ordered except the Warmoth parts but supposedly something from reverb is showing up in a day or two. I used Apple Pay on my reverb purchase for the $100 amount but it was not used on the $500 order in question though it posted to the same CC.