Help!!!!

Only way to regain entry to your account is via account recovery -- Recover your Apple ID when you can’t reset your password - Apple Support or if you generated recovery key you can use that to regain entry -- How to generate a recovery key - Apple Support.

Not necessary the account recovery is to be done every time , if one remember the old trusted number ( say 1234.... ) that is inactive , the person can visit the cellular service give his identification proof and issue a sim on behalf of the same number and insert the sim https://support.apple.com/en-in/guide/iphone/iph3f11fba92/ios in new iPhone that is purchased https://support.apple.com/en-in/guide/iphone/iph1fd7e482f/ios

The Apple ID and password is active so is the 2FA active on the iCloud server , once a new trusted number is added the code will start appearing on the new trusted number , and the person can access the account .

See the article  https://support.apple.com/en-us/HT204974

Once the account is accessed remove the old trusted number from the account that will be still visible .

Add or remove an SMS number

1. Go to your Apple ID account page and enter your Apple ID and password.
2. In the Security section, click Edit.
3. Click Add a Trusted Phone Number. 
4. To add a number, enter the phone number and verify it with a text. 
5. To remove a number, click  next to the phone number you want to remove.