I should remove my credit balance

Hello ~ Take a look here:

Change your Apple ID country or region - Apple Support

You can make a purchase of something in App Store for more than shown. The remaining will be billed to your credit card on file…thus leaving you with a zero balance . You may also contact Support from above link or by going to the lower left and click on Support and they can also help. Also:

Contact Apple for support and service

~Katana-San~

The options available to you are...

1. Add more funds and buy something useful else
2. Learn what to do if your remaining store credit is less than the cost of a single item.