I am not sure if they are open today or not, but in order for the points not to go into "holding", you must cancel 31 days or more ahead of time.
I am hoping that you meant today is day 31 and not day 30. If it is, you may already by too late.
But, sending an email would be a great idea as it does show your intent to cancel today. MS might have leeway in this case, a holiday, to make adjustments.
Good luck and I hope everything works out for you!!!