About three weeks ago, Apple forced me to change my Apple ID password. I have setup my new password on my iPhone and two iPads. However, since that change, iMessages and text messages only arrive on my iPhone. Prior to password change, iMessage would message all my iDevices simultaneously. What gives?
Apple will never force you to change your password unless you type your password in correctly too many times.
If you were prompted to change your password, then it could have been a scam.
Assuming it wasn't a scam, you will need to make sure each of your devices is logged in with the same Apple ID. I you changed your password but only logged into one device, the other devices won't work. Use this article to learn how to properly set up iMessage with your Apple ID. I would make sure each device is using the same number/email address for iMessage and make sure iMessage is using the same Apple ID for all. To be even more sure, go to Settings > Messages > Send and Receive and log out of the Apple ID on each device, and then log back in using the same Apple ID.
Also, including the device and iOS version you are using is very helpful. Can be hard to troubleshoot a device if we don't know which your device information. I wouldn't give you advice on how to change your oil if I didn't know what kind of car you drive...
https://discussions.apple.com/static/apple/tutorial/ask.html
imessage stopped working after apple forced me to change password
