OP, why can you not sign into the gmail account which you used to set up your main eBay account?

Have you forgotten the password for that?

It is troubling if you’re in that situation because it’s exactly the sort of scenario which would raise suspicions of unauthorized access.

Don't you have a password recovery email address set up?

What about security questions?

Check this page for the various ways to reset your password on the gmail account:

https://support.google.com/accounts/answer/183723?hl=en&co=GENIE.Platform%3DDesktop&oco=0

You cannot blame eBay staff for not magically enabling access to your account. They’d be at fault if they did enable access under the current circumstance when you can’t prove your identity via phone or email.

I would really move heaven and earth to access that gmail account.