I havnt got my old number I signed up with keychain. How do I change this?

See if this helps --

1. On your iPhone, go to Settings → iCloud → Keychain and switch Keychain off then on again.
2. Tap "Approve with Security Code", tap "Forgot Code" and then tap "Reset".
3. Follow the instructions to reset iCloud keychain and create a new passcode.You will then be prompted to update to your new number.
4. You will then be prompted to update to your new number.

You're most welcome! 🙂