Why does the iPhone 16 Pro keep saying "Call failed"?

Hello all,

I'm an iPad user and recently purchased an iPhone 16 Pro. Initially, everything worked perfectly—I had no issues at all. But lately, I've been facing a frustrating problem that's driving me crazy.

Whenever I try to make a call, the phone just says "Call Failed." I use two phones on the same network, and the other one works just fine. I've attached pictures of the signal strength on both phones taken from the same location.

Here’s the issue: once this problem starts, I can’t make or receive any calls. Incoming calls don’t reach me either. I’ve ended up checking every 30 minutes by calling my iPhone from another phone—just to see if it’s working. Obviously, this is not sustainable or practical.

Before I get too aggravated and do something drastic—like returning the phone and switching to something else—I want to check if there’s anything I can do to fix this.

Here’s what I’ve tried so far:

• Restarting the phone (fixes the issue temporarily)

• Making calls through WhatsApp (works even when normal calls fail)

• Toggling Airplane Mode (does not fix the issue)

• Checked Focus Mode (not causing the issue)

• Moved to different areas (once the issue starts, location doesn’t help)

• Updated to iOS 18.3.2 (pretty sure this is the version; I can share a screenshot)

• Tried the Apple Diagnostics app (gets stuck on “Cellular Service” phase)

• Reset network settings (problem still persists)

Honestly, I no longer have the time or energy to fiddle around with this like I used to. Work is already stressful enough—the last thing I need is the added anxiety of wondering whether my phone is even working. 😞

I’d really appreciate any advice or suggestions you might have.

Thanks in advance.

[Edited by Moderator]