Unable to change my date of birth

I was recently hacked but was able to get my account back. Everything has been fine and there has been no signs of the hacker trying to get back in as I have changed my passwords and ensured two factor authentication everywhere. I was able to change my name back to what it was but have done everything I can to try and change my DOB but it’s not working. I keep getting a message that the service is not available at the moment. I would really appreciate help in this as Facebook is notifying ppl that it’s my birthday on September 23, when that is in fact not my birthday.