How can I disable iMessage for a phone number if the iPhone it's attached to has been destroyed? My sister dropped her iPhone in the bath, so she is now using an older non-Apple phone. Whenever I send her a message, it gets sent as an iMessage (and even says "Delivered"), but her device never receives the message.
The only information I could find was this Apple knowledge base article which states the following:
If you plan on transferring your SIM card or phone number from an iPhone to a device that does not support iMessage, turn off iMessage in Settings > Messages first. If you do not, other iOS devices may continue to try to send a message using iMessage first, instead only using SMS or MMS.
However, since this iPhone was destroyed, we can't get into the settings to unregister her phone number.