Is it because your OneDrive storage is full?
If so, has it been 48 hours yet since you purchased the subscription? If not, it can take up to 48 hours for the changes to be reflected in your account? If it has been more than 48 hours, you would need to contact Microsoft billing support. 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.