Treatment of Non-Refundable Income after cancelling an Invoice

Treatment of Non-Refundable Income after cancelling an Invoice

A customer made part payments of 30,000 for an invoice 0f 100,000, and then he is unable to pay up the remaining and has asked for a refund.
As per company policy, he can only get 75% of the amount paid, which is 22,500.

The remaining 7,500 is non-refundable income.

After refunding the 75%, the remaining 25% is showing as unused credits in the customer's profile.

How can I move this remaining 25% to Non-Refundable Income account?