I am not an expert, especially recently with how much is changing - but start with the reservation, look under cancellations, on the right side options, "report user" might be your only option to get to general "Airbnb Help". They make this not easy for hosts. Keep trying, yes, phone support numbers will pop up eventually, if I try to type one, it may block it into xxx-xxx-xxxx - Did these guests provide photos? Go to resolution center, follow up, chase this issue down, it takes a while, but if there are photos, you gotta accept what you see - and you have a right to ask to see them - but if no photos? Push back. Everyone is trying to find an ant after they had some time at a listing, and use it as an opportunity to get money back like we are all some corporate hotel chains who won't miss the money. It wasn't like this until 2020.
Sincerely, push on, it takes time, be firm yet polite always, and good luck.