AppStore credit

Have you contacted iTunes - Official Apple Support

Like I said in the previous message? They can help you zero your balance, we as fellow Apple users on this forum (this is an user support forum) cannot

We are mostly users like you, not Apple employees, so we don't have access to any data information.

Contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

Apple on Twitter

If the balance is less then the cost of a single item, you can ask iTunes support staff to zero your balance

iTunes - Official Apple Support