Buy something more expensive and pay the balance with a credit card or contact iTunes Support and ask them to zero balance your account.
See the Apple Support articles below for contact information.
iTunes Support – world wide
Apple Support schedule phone call
Billings and Subscriptions
If necessary, try Twitter
https://twitter.com/AppleSupport. People have posted it may take an hour or more to get a response.
You need a zero account balance and you need to cancel all your subscriptions. If you have cancelled all subscriptions, but some haven’t expired, contact iTunes Support. You need a valid credit card issued by a bank in the country the store is in and you need a billing address in that country. If you have an account balance, either buy something more expensive and pay the balance with a credit card or contact iTunes Support and ask them to zero balance your account.
Purchases - View, change, or cancel your subscriptions.
Purchases - Subscriptions not billed through Apple
Purchases - the subscription that you want to cancel is not listed
Region - Change your iTunes Store, iBooks Store, or App Store country or region.
If necessary, contact iTunes Support. Follow through the screens to get a chat or telephone option.
iTunes Support – world wide
Apple Support schedule phone call
