Hi Charles,
i have the exact same problem, I have been trying all the tricks from all the forums for 10 days now... Very frustrating...
had an iPhone 5s on my old number A, got a new iPhone 6s, restored it from iPhone 5s back-up. Using now a new SIM card with a new number B in a new country. Every time I try to reactivity iMessage, I get in greed out roaming my old number B showing in the list, my email is activated properly on both iPhone/iPad/macbook. Only email shows up in iPad and MacBook. But nowhere I can get the new number B, either facetime or iMessage.
I Have also tried to deregister, but the tool is silly... It is sending you a code on the number you want to deregiste... So of course I can't get it...
IT is very frustrating, especially when all post and help tell you the same thing and when you can see you are not the only one stuck...
HELP much appreciated... Thanks