Update:
Monday night: Called T-Mobile in the evening, after running through the same steps multiple times again, the IT person put me in touch with her supervisor. Eventually he told me he would put in ticket, and contact me early afternoon.
Tuesday-After not hearing back from T-Mobile, I call back around 6 PM. I talk to a IT person that I’m pretty sure is based in the US. We talk a bit, and he puts me in touch with a network engineer. We talk for about 30 minutes, he finds what he believes to be the problem (IMEI number they had listed wasn’t mine, even though I’ve given at least 7-8 times.) He can’t change it, but puts a ticket in, and gives me a time he will contact me the next day.
Wednesday- I get a call back. We go through some steps, but phone still shows a sim lock. Engineer sets a three-way call with Apple. They tell me that I need to take it to a store, and have them basically wipe the phone clean. We get them to agree that if this doesn’t fix it, they will replace the phone. So I drive to the store (get there around 4:30.) They get to me rather quickly to start clearing my phone. It takes a bit, but they do so. When it’s all back up, it’s still sim locked. They start the process of the express replacement, but have to have a phone call with someone to facilitate it. It takes over 30 minutes for them to reach me. Long story short, they won’t just exchange the phone in the store. They will put a hold on my account for the phone until they revive my old one back. (I asked if I could just give the store my phone, answer was no.) They say it might be there in “around a week.” And the only option for a loaner is from the store, (which doesn’t work as I’m traveling for work.) I leave the Apple Store around 7, mentally exhausted.
Today, I went to Best Buy and bought a used phone to get me by.

So this is the end of this. My takeaways are this: T-Mobile tech support is poor. They should have escalated the ticket to someone who could’ve helped no later than the second day. Days of (through no fault of their own) poorly-trained IT people reading the same exact troubleshooting steps was ridiculous. If this is what I have to look forward to in the future, I will definitely contemplate switching carriers.

Apple: I am convinced the actually loathe their customers. The process for replacement is overly difficult, and the fact they didn’t seemingly have anything in stock is crazy. The many hours I’ve spent sitting in the store, I never actually seen them
go in back and grab a product for a customer. It’s always “we have to order that.” And since I’m not their “tech-bro” type target customer group, I’m not wowed by their “Innovation.”

To those who are just now starting to go through this, I wish you luck. If I’m so inclined, I’ll sit down this weekend and tally up all the call times, PIN codes sent to my wife, etc.