https://learn.microsoft.com/en-us/partner-center/mpn-benefits-azure-cloud

When you assign the Azure bulk (yearly) credit, the Remove option isn’t available in Partner Center. Instead, you need to transfer the bulk credit to someone else during your enrollment year. This type of credit subscription also can’t be combined with other licensing, prepaid, or credit offers (for example, the Microsoft Enterprise Agreement, Cloud Solution Provider, or Azure in Open). Reach out to support to transfer bulk credits.

Your ‘Azure Sponsorship” Subscription in Azure should say :

Offer : Azure Sponsorship

Offer ID : MS-AZR-0036P

If it still says the below contact Microsoft Support

Offer Pay-As-You-Go

Offer ID Unauthorized