@Diane749 Doesn't sound like Airbnb is trying to help with this problem at all..
From what I gather from your comments ;
1. The guest payment never went through
2. Airbnb cancelled their reservation
3. The guest is still at the house
Has Airbnb not reached out to the guest advising them their stay was cancelled and they are to leave the property?
If Airbnb cancelled this reservation, I would be surprised if they reimburse you for the costs of the guest still being there.
I'd ask the guest to leave myself (bring a friend with you) and if you run into an issue, then call the police.
This does not sound normal for Airbnb and most definitely could be a scam (from the guest).