I can’t seem to change my Apple ID and everything to change country Australia to New Zealand had nothing but trouble and can’t get apps

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