I need to change my country/region to be able to process my payment

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    *

Link to contact Apple Support at the end of the article.

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 you have done all the above and are still having problems, contact iTunes Support. 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.   -