To me it isn't clear to which phone you are now having this sent. You don't have your old phone. You don't have your new phone "until it is ready".
Review your numbers an make sure it is there:
To see, add, or change your trusted phone numbers use one of these methods:
● On your iPhone, iPad, or iPod touch: Go to Settings > your name > Password & Security. Next to Trusted Phone Number, tap Edit.
● On a Mac computer choose Apple menu > System Settings (or System Preferences), then click your name (or Apple ID). Click Password & Security, then add or remove a trusted phone number.
● Using a web browser: Go to the Account Security section of https://appleid.apple.com
Make sure the software is up to date on all devices involved.
Make sure notifications haven't been disabled. This article discusses notifications --> Use notifications on your iPhone or iPad - Apple Support
Sometimes it helps to have the devices involved take a fresh look at settings:
● Try signing out of accounts and back in again.
Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac - Apple Support
Sign in with your Apple ID - Apple Support
● Restarting is a simple step that can resolve many unexpected behaviors.
iPhone: Restart your iPhone - Apple Support then choose your model.
iPad: Restart your iPad - Apple Support
Mac: Ways to start up your Mac - Apple Support
If a problem persists, particularly over several days, try contacting Apple for assistance:
Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
"See a list of Apple phone numbers around the world."
Click here --> Contact Apple for support and service - Apple Support