I thought I was the only one having issues with Vestiaire but obviously I'm not. I have sold two items there before and all worked fine, but now they have not paid me for the shoes I sold on 20th Oct. I sent the shoes immediately of course and got confirmation that they have received and accepted them, but no money. Last time I asked, they told me they would pay on 30th Nov, but till now, I have received no money. If they won't pay fast now, I think I'll stop all my business with them.
I never had success in calling them but when I complained on the FB page, I was paid promptly after. See if it works for you.