Due to the coronavirus crisis we've had to move to an appointment only basis, probably for the foreseeable future. You can make appointments via Apple's Support pages:
Please note that currently appointments are filling fast. This isn't unexpected - if you can't see any available appointments there won't be any that the staff can offer over the phone. Appointments open on a hour by hour basis, and are only available a week in advance, so for example a 10am Wednesday appointment for next week would open up at 10am this week.
If you have an existing repair you can contact the workshop staff via your ticket link or call at 02890 832600.
Thank you for your patience and understanding.