iPhone bought in Europe

Had iPhone X for several years, moved to Europe on work visa, had to get new phone immediately. Put my SIM card into new iPhone and now I keep getting a message that my SIM card is locked up. I contacted phone carrier and they told me they are not able to activate phone to my account. I asked why and he said the IMEI number won’t allow him to register. I don’t understand I’m not changing anything on account, an iPhone is an iPhone. It was purchased from a very well known reputable electronic store brand new never opened. Is there anything I can do?