I can't change my payment method because I can't change my country to the one where I live now

See Change your Apple ID country or region https://support.apple.com/en-us/HT201389See this heading especially What to do before you change your country or region

Use this link in the document if you need to View your Apple ID balance https://support.apple.com/en-us/HT202359

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. Note that you could just purchase something of value greater than or equal to the amount of your store credit or ask iTunes Support to zero out your account balance using this  iTunes Support Form https://support.apple.com/en-euro/itunes-contact

And you also can contact iTunes worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunesChoose your country. At the bottom of your screen use Tell us how we can help to select among support options. You should be able to get telephone or chat support.

What happens when you try? Error message(s)?

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 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     

Region - Change your iTunes Store, iBooks Store, or App Store country or region.     

If necessary, contact iTunes Support. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option.  

 iTunes Store - Contact Us - Official Apple Support.       

iTunes Support – world wide