My physical SIM is not working, after deleting my eSIM

I bought a new phone and it asked me to transfer my number as an eSIM. I followed the instructions, and everything worked. As I downloaded my apps and other content, I realized that I didn't need an eSIM, so I deleted it. I just wanted to take my physical SIM out of my old iPhone and put it into the new one (which is still possible in Europe). However, after I deleted the eSIM and put the physical SIM into the new phone, it stopped working. Now, I have no connection for calling or internet. How can I solve this problem, or did I break my SIM by adjusting the settings?

[Re-Titled by Moderator]