cannot make or receive call

I was in the middle of exchanging my new iPhone 13 pro max for another one I was sent through the mail. I was working with Apple support but during set up we were disconnected. I tried calling them but the call failed each time and then I realized all calls are failing. So I can’t get support and I don’t know what to do next but I’m also in a time sensitive spot as they need my old phone back soon so I’m not charged for both phones.

I appreciate your responses!