Using Classic Outlook on Windows for personal email, calendar, and contact management
Hello
Can you go to https://account.live.com > Subscriptions, and make sure you have one of these plans:
Personal | Family | Premium
And make sure the plan is active and not expired.
If the plan has been purchased lately and if it hasn't been 48 hours yet, just give it time as it can take 48 hours for the storage to update.
If it has been more than 48 hours, you need to contact support to have them fix the provisioning. To get help, open the "Get Help" app on your computer (just search for it in the Start menu). or go to https://support.microsoft.com/contactus, Type "Billing" and press Enter. On the next screen, click "Contact support" at the bottom of the page, then choose "Microsoft 365" > "Manage my subscription". You’ll then see the option to chat with a Microsoft support agent who has access to your account to help review the issue.