Wow, this has been going on for at least a year. I can't believe that Apple hasn't already fixed this problem, it really calls into question their commitment to doing the right thing.
Does that work if you've wiped and resold your iPhone without disabling iMessages on it first? The impression I've gotten is that Apple will still think you're signed in even though you no longer have the phone (and can't sign out).
Yeah I tried that one too. Deactivated my number on imessage on my phone and turned it off everywhere else I used it. People sending me texts still send as imessage rather than SMS and still show as delivered on the senders end. My new HTC never gets any of it. Even worse none of my existing imessage devices get the message either. It's simply gone. An Apple support rep actually suggested that I have everyone that I text with delete their conversation thread with me in their app in order to fix the issue. Seems like an unreasonable burden to put on the user. Needless to say attempting that on a few friends phones did not seem to work.
Sometimes this process just doesn't work. I've switched to android twice (and back to iPhone) in the last year cause of phone breakages and the moving off of iMessage the second time was a nightmare.
I've done all of that. The number is no longer associated with my Apple ID, but other iPhones still send messages to that number via iMessage — which means they go nowhere.
Well shit. Sounds like Apple has an issue clearing cache.
In the hopes of actually solving your issue, I hate to suggest this, but try reconnecting your number to imessage (and make sure you get any new imessage texts), then properly turn off imessage from that device. The defacto unplug it plug it back in.