Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
I understand how frustrating this must be, especially after the phone support system repeatedly redirected you to online assistance. I'm just another user here on this public forum, not your organization's admin, so I'm not able to reset or unlock anything on your account myself.
First, I would not assume that the old Volume Licensing account automatically became the Global Administrator for your current Microsoft 365 tenant. The account used for Volume Licensing and the tenant’s Global Administrator may not necessarily be the same account.
Since you can still sign in with a standard user account, could you check whether you can access the Microsoft 365 admin centre and whether the account has any limited administrative role? Also, please check internally whether another employee, former IT provider, Microsoft partner, or reseller may have been assigned a Global Administrator role.
If no accessible Global Administrator exists and the old administrative account cannot complete password recovery, a standard user cannot promote their own account to Global Administrator. You will need to contact Microsoft Support and request escalation for Microsoft 365 tenant recovery.
Because the phone line is not supportive, you can consider directly submitting a support request as a helpful workaround:
Consider signing up for a trial subscription to create a new tenant. Visit Microsoft 365 Business Plans and Pricing | Microsoft 365.
Once the new tenant is set up, you can access its admin center and submit a support ticket through Microsoft 365 admin center > Support > Help & Support to contact the Data Protection team regarding the previous tenant. Please remember to cancel the trial subscription after your issue is resolved, as this will help you avoid any accidental billing. You may prefer the following resource for detailed instructions: Cancel your Microsoft business subscription in the Microsoft 365 admin center | Microsoft Learn
I hope this helps point you in the right direction. If you have any updates or additional questions, feel free to reply back and I'll do my best to assist further.