Bookings Custom Availability

We are using a calendar for multiple site each with their own service and custom availability. 

We close the bookings for a particular service at a specific T- date by removing the custom availability, general and system availability is set to Not Bookable yet even with custom availability deleted, appointments can still be booked.

Setting a minimum lead time does not work well for us as a site could have appointments available over a number of days we need to stop any new bookings for a specific date using say 48 hours Minimum lead time still enable bookings on day 2 or three etc...

The main point is that removing the custom availability does not prevent new bookings being made despite all other setting saying Not Bookable - 

Can anyone offer anything else I should try?