Apple ID cents

As macjack says, in effect, you could purchase something of value greater than or equal to the amount of your store credit or try to get Apple Support to zero out your account balance using this link https://getsupport.apple.com/?caller=cups&PGF=PGF63006&category_id=SC0060&symptom_id=23330 (different from the one macjack posted)

The link eventually comes from here: Change your Apple ID country or region https://support.apple.com/en-us/HT201389. This document says: If you can't complete any of the steps, can't change your country or region, or you have less store credit than the cost of a single item, contact Apple Support

If you can’t use it, you can contact the iTunes Store and ask them to zero it out.

https://www.apple.com/emea/support/itunes/contact.html