Unable to login to SC "We cannot find an account with that e-mail address"

hello folks,
every time logging as secondary user in SC with e-mail like My.Name@Company.com and was providing all legal information to get my seller account verified as a business, successfully.

Now, I’ve realized that I’ve registered initially on SC with my whatever@gmail.com and I want to change it.
However, when I try to login to SC with my whatever@gmail.com I get error “We cannot find an account with that e-mail address”. Opened numerous cases which not much of success. No error in the e-mail. I am doing careful copy-paste.

Cleared cookies and all offline content, restarted, no help.

What can I try to be able to login as primary user?