unauthorized charge and airbnb won’t even tell me what I’m expected to pay for

Checking my credit card statement recently I noticed a $100 charge from airbnb. I didn’t go anywhere. I called airbnb, actually got to talk to someone, and later received an email saying that airbnb found the charge to be “legitimate”!!!! No, I did not authorize this charge. So I asked them, well, where did I go? THEY WON”T TELL ME! What a business model–charge your customer but don’t tell them what they’re paying for. airbnb told me I would need a subpoena to get the information.