Unfortunately, the only way to regain access is to use a working verification method (such as the verification email/phone/authenticator) or successfully complete the Microsoft account recovery form.
Please note that account recovery can only be completed by the account owner. I understand this may be a special situation, but support agents can’t bypass verification or override Microsoft security policies. If the account owner cannot complete recovery and access is required due to legal circumstances, it would need to be handled through the appropriate legal process, since support can’t violate Microsoft policies.