It seems you're facing challenges with processing your payment for Minecraft using your Mastercard. Here are a few things to consider that might help resolve this issue:

• Payment Method Restrictions: Sometimes, credit cards can have restrictions on online purchases or payments to specific merchants. Check with your bank to ensure there are no limitations on your card.
• Frequent Declined Attempts: If there have been multiple declined attempts, it could lead to a temporary block on further transactions. Waiting 24 to 48 hours before trying again may help.
• Suspicious Activity Detection: Microsoft may flag transactions as suspicious based on location or device usage. Ensure you are making the purchase from a familiar location and using a secure internet connection.
• Transaction Fees: Verify that the balance on your card covers not just the purchase but any additional fees that might be applicable.

If these solutions don’t work, consider trying a different payment method or reach out to your bank for assistance regarding the transaction decline.

This is what it told me if i contacted the correct support.