I spent $300 on an second hand dress

And the seller got the money as I have proof I sent it but they wont post the dress because they have issues with their paypal account they wont sort out and keep making out I havent sent the money when I have. I have proof I sent it so I shown them. My event is this week and I still dont have an evening dress. I might have to wait an month before I can get the dress thats if they even send it. I dont know what to do because Ive already paid for the event and I cant afford another dress because I havent been at work this month.