Apple watch ultra different models for America and Europe

I bought an apple watch ultra in America at Apple Crabtree Valley Mall. I told the seller that I was buying to use in Europe and he assured me that everything would work. However, when returning to Europe, the watch does not connect to the Telia network. The network operator explained that the reason is different models for Europe and America and I will not be able to use the networks in Europe. I have been an Apple user since 2007. I feel cheated and no one can solve this problem. The store I bought from does not respond to emails.
Maybe someone can advise me what to do? Is it possible to solve this programmatically? Where do I go for help to change my Apple to another model?
Even Apple's presentation doesn't mention anything about it. I thought it would work worldwide like the iphone. I go to another country and buy a phone sim for that country. And does the apple watch Ultra need to be bought separately for each country?
I'm asking for help.

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