I have no service providers available, but the site is still allowing appointments to be made

Hi,

I have my appointments set up and my exceptions are scheduled. My problem is that I have no providers scheduled, but people can still make appointments at that time. For example, I have 4 service providers working from 9:00-10:30 daily, but none of them are working on the 23rd. However, you can still make an appointment at that time. Obviously, if there's no one working, there's not going to be any service provided. How can I make sure that's not happening?

Thanks,

Jen