Apple Pay money
I changed my Apple ID and my money is gone. How do I get it back
Did you actually change your Apple ID (https://support.apple.com/en-us/HT202667), or simply create a new one to use?
If you created a new ID you'll find everything still connected to your old ID; accounts cannot be combined and it's not a good practice to have multiple IDs.
If you simply changed your Apple ID, you may wish to contact Apple Support.