Only the USA could possibly have Jobcenters. We spell them Jobcentres.
The entire Civil Service will be taking the bank holiday off so it will be closed. You should have an appointment, and it is quite normal over bank holidays to miss one, especially with more than one in a row - they will have been closed on Good Friday too. Certainly they will have been unable to book one for tomorrow on the computerised appointment system. So what does your appointment card say?
It is a bank holiday so it is going to be closed... phone them first thing in the morning and either listen to instructions about sign on day and/or leave a message 0845 604 3719
Public service offices are all closed on bank holidays.
In the UK the word is "centre" not "center".
The Job Centre will be closed on a bank holiday.
It is a Bank holiday , like everywhere else it will be closed.