Here is what Yahoo saying for cases similar to yours:
We take your account's privacy and security very seriously, and we'll only let you reclaim an account if you can prove you're the rightful owner.
When you register for an account, it's up to you to provide the most up-to-date and valid recovery info. Your best option to avoid losing access is to update your recovery info if you get a new phone number or change your alternate email address.
The Password Helper says my password can't be reset online - If you've tried using the Password Helper and weren't able to get access to your account, other recovery options may not be available. We know it can be frustrating to see the fail page, but in these rare cases, we recommend creating a new Yahoo account.