Breaking up with your iPhone soon? Beware: your new Android phone may not be able to receive texts because they may be trapped in iMessage.
A major iMessage server bug  can't tell which phone numbers are associated with Androids and is holding texts captive in Apple's cloud. Apple is working on fixing the bug, but in the meantime, read on for some quick-fix solutions to the iPhone-to-Android problem.
On any iOS device (iPhone, iPad, and iPod Touch), open the Settings app and turn iMessage off to deregister your phone number. If you can't access your iPhone (because you sold it or gave it to someone), contact Apple Support .
Deactivate Messages for Mac
In the Messages app for desktop, go to Preferences, select the Accounts tab, and deselect the "Enable this account" checkbox.
Changing your Apple ID, resetting network settings, or removing your phone number from My Support Profile  will not fix the iMessage problem. Good luck!
Source: Apple