Hi Ann,
Thanks for contacting us!
I’m very sorry about this issue you are experiencing. The first thing we need to know here is why you are getting a 500 internal server error every time you press the customize button. Your hosting provider should be able to help by sharing the PHP error log with you. Another way to figure out the culprit is by disabling all of your plugins/changing your current active theme and checking if the issue persists after that.
Regarding the monthly display issue, it is working properly as I can see from here. Can you please check and let me know if everything is working as expected from your end as well?