By going to the Yahoo Mail website on a computer, you can select the Trouble Signing In button below the sign in boxes and enter your yahoo email that you are having trouble accessing. If you do in fact have this number listed as a recovery number, all you would need to verify is the digits that are blanked out on the next screen and then it should give you the option to verify your email address that you are trying to log into and then you can change the old number to the new number that you now have access to.
Hope this helps your situation! You don't need to hire me for this. :-)