SIM card problem?

Hi! I am studying abroad in Italy this semester and have just been using wifi to send my imessages and communicate with people back home in the states. I recently bought a SIM card through the company TIM and it worked fine for data for when I was traveling. I decided to switch back to my American SIM card so I could send messages from the actual number but now they are only being send from my email and the only phone number that comes up as an option is the Italian number linked to the old SIM card. I have tried resetting my phone and taking the SIM card out and back in and still nothing. Anyone have any clue how to fix this?

I tried turning Imessage on and off and it just had a message that it was waiting for activation for hours.

Thanks in advance!