Things you can do yourself.

Not everyone is aware that there is an on/off switch on the rear of the clock - check that you haven't inadvertently switched your clock off. 

Are the batteries good and fitted correctly?

Cycle the flaps though a full rotation - cycle a full week, month and year, then see if your clock works.

If you you still have a problem after running through the above , get in touch, but before you do, please check the following and include your findings in any contact?

Does the clock whirr as it passes 11:20 (this time can vary slightly) and does the day advance at 12 o'clock?

Does advancing the day cause the date to advance?

Does taking the date beyond the end of the month cause the month to advance?