Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Thanks for your confirmation.
Since you were able to successfully create an onmicrosoft.com account, this is likely the Global Administrator account for your Microsoft 365 business tenant. I recommend signing in with that account and attempting to access the Microsoft 365 Admin Center.
Once signed in, please create a support request by following the instructions in the Microsoft Learn article below: Get support - Microsoft 365 admin | Microsoft Learn
Please let me know whether you're able to access the Admin Center and successfully submit the support request. If you encounter any errors during the process, feel free to share a screenshot or the exact error message, and I'll do my best to assist further.