Multiple Bookings at the same time when there is not availability

Hello, We have been using microsoft bookings for a few years now and are able to usually work through the glitches it has from time to time, but we have not been able to find a solution for the current issue. Bookings is allowing customers to book 100's of appointments for times that are already full. We have had to shut days off to help manage the issue, but it is becoming a bigger issue. I have submitted feedback through microsoft but have been unsuccessful. Can someone point me in the right direction?  Thank you,

Rick