I had the same issue. Booked a large group trip in February for July of this year and I was charged the remaining amount on 4/27 without my consent despite email confirmations showing the balance would be charged in late June. I've talked to customer service three times since then and they won't refund the charge to me. They said they're aware of the issue and should have it resolved in a couple weeks (as of today). I'm disappointed with the company's refusal to provide a prompt refund for their error and putting a burden on their customers.
They gave me a coupon for a future stay, but I'm not sure if I'll be using Airbnb again after this experience.