"Cannot connect" calls on Samsung S20+

I'm posting this here as documentation for others who have the same problem. I've nearly accepted there is no fix.

TL;DR: When I am near my home location, my phone shows "Cannot connect" when trying to make outbound phone calls, and incoming calls just send straight to voicemail. I've had this issue since I got my new unlocked phone, I've spent 20+ hours troubleshooting, ATT has been worthless, and Samsung did not fix it when I mailed it in to them.

The issue:

When I am home, or near my home, and try to make a call, I receive a notice "Cannot Connect" on my unlocked Samsung S20+ seconds after hitting the call button. This does not happen every time I try and call, but 90% of the times. Everyday, if I want to call someone, I will have to press "call" about 25 times for it to go through.

With inbound calls, I believe it just goes to Voicemail, and I never receive notice of their call.

Things I've tried

• Restarting my phone

• Resetting network settings (multiple times)

• New sim card (four, to be exact) (5g and non-5g)

• Updating my IMEI and ICCID (multiple times)

• Asking ATT to open a ticket/contact me (no luck, no contact)

• Factory resetting phone (multiple times)

• Calling/chatting/visiting ATT (so many times and so many hours)

• Screaming and yelling by myself, into the air

• Begging (multiple times)

• Modifying Access Point settings (nxtgenphone)

• Speaking to Samsung repair shop (uBreakiFix)

• Sending phone into Samsung for them to repair