My credit is gone after creating a Nintendo Network ID. What to do?

I'm really desperate right now! I loaded funds into the Nintendo eShop on my Switch. Then I wanted to merge the credit with my Nintendo 2DS XL but you need a Nintendo Network ID, which I then created. I then set NNID at my Nintendo as a registration option. Before I registered with my email address, now I have changed it so that I only need the ID to register. When I looked at the switch for the credit to merge it with my DS, the money was gone and I had credit of 0 euro. Where did the money go How do I get it back? It just annoys me a lot and makes me despair… Can someone help me?

The money is in your other account that you previously had on the switch.

OK? But it's actually the same account, only with Nintendo Network ID. Do you know if I can get the money over somehow? Without a NNID, I can't combine the credit.

I don't really know about the Nintendo system, but the money has to be somewhere. Do you still have it on your switch? Or is it completely gone?