Why doesn't my iMessage recognize multiple number from the same contact?

It sounds like you're encountering a frustrating issue with iMessage. Here are a few steps you can try to resolve the problem where iMessage isn't recognizing multiple numbers from the same contact:

1. Check Contact Card: Open the contact "mon Chéri" and ensure that both numbers are correctly listed without any duplicates or extra spaces. Sometimes formatting issues can cause confusion.
2. Delete and Recreate the Contact: Delete the contact completely and then recreate it. This can sometimes help clear up any underlying issues.
3. Update iOS: Make sure your iPhone is running the latest version of iOS. Apple often fixes bugs in updates, and your issue might be one of them.
4. Reset Network Settings: Go to Settings > General > Reset > Reset Network Settings. This will reset your Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before, but it might help with iMessage issues.
5. Sign Out and Back In to iMessage: Go to Settings > Messages > Send & Receive, tap on your Apple ID at the top, and select "Sign Out." Then sign back in.

If all this advices did not work, then I would like to recommend you to call Apple Support Service: Contact Apple for support and service - Apple Support (IL)