Apple subscription

If you want to clear your Apple Balance, you can buy a product in e.g. the App Store or iTunes Store which costs the amount you have left. If the amount does not match a purchase, then the rest will be deducted from your credit card or other payment method you have associated with your Apple ID.

If you don't have other payment methods associated with your Apple ID and don't have the option to add it. Then you can contact Apple Support, who can help you reset your balance.

Contact Apple Support here:

Contact Apple for support and service - Apple Support

I have not tried to be in the same situation myself. But I believe it is something they can fix on the spot.