Hello dl_79,
Thank you for using Apple Support Communities. It's my understanding that messages received from a recently updated contact appear with the old contact information. You've done a great job trying to get this resolved. I'm happy to help.
If you haven't already, I recommend using the steps below to deleting previous conversations from the old contact and test the issue again:
" When you delete a message or conversation, you can't get it back. So make sure that you save important information from your messages.
To delete a message:
- In a message conversation, touch and hold the message bubble that you want to delete, then tap More.
- Tap , then tap Delete Message. If you want to delete all messages in the thread, tap Delete All in the upper-left corner. Then tap Delete Conversation.
To delete a single conversation, swipe left over the conversation that you want to delete, tap Delete, then tap Delete again to confirm. To delete more than one conversation, open Messages and tap Edit in the upper-left corner. Then tap the circle next to the conversations and tap Delete in the bottom-right corner.
To keep your messages for a certain amount of time, go to Settings > Messages > Keep Messages. Then select how long you want to keep your messages."
Use Messages on your iPhone, iPad, or iPod touch
Let us know the results. Please include any other troubleshooting steps you may have tried.
Have a nice day!