They literally replied to his registered email and he has the reply. That would indicate that he has at least access to the account. So with OP’s next email quoting the reply ownership over the associated email address should be reasonably established.
They literally replied to his registered email and he has the reply. That would indicate that he has at least access to the account. So with OP’s next email quoting the reply ownership over the associated email address should be reasonably established.