@Beth408 A lot of hosts have been reporting this here recently. It's obviously a system glitch that is affecting some accounts, but it doesn't seem that Airbnb is admitting that it's an issue. Either the dates show as available on the host's end but not on the guest's, or they show as available to the guest, but when they try to book, they get a pop-up that says the dates aren't available.
All I can suggest is that you be persistent with CS and let them know that other hosts have been reporting this on the community forum as well, that it's not just an isolated problem on your account.