Hey lucinda32,
Thank you for using Apple Support Communities!
I understand from your post that after changing your region, you were unable to change your payment method. I'd be happy to help out.
Keep your device updated along with making sure the payment method you're using can be used with the Apple ID: Payment methods that you can use with your Apple ID
If it's possible, also try another Wi-Fi network connection or switch to cellular/mobile data to see if you still get the error.
I would also suggest, signing out of the iTunes & App Store or App Store depending on your device, restart the device and then sign back in.
Here are some great articles with additional information:
Change your Apple ID country or region - Apple Support
How Apple uses your payment information
If your payment method is declined in the App Store or iTunes Store - Apple Support
Cheers!