Q: my iphone doesn't work after changing cards from us to polish ones

Hi, I've got a problem. I took my iphone 5s from usa to poland i put polish card and everything was ok but then i changed cards twice and my iphone is blocked now. It says it is not the fault of the phone but i should install the card SIM which is serving but when i put an American card it is also the same i hope you can help me to deal with it.