iPhone 11 lock issue

I'm helping a co-worker with her iPhone. She purchased an iPhone 11 Pro Max at Target in November of 2019. She paid full price for an unlocked phone. The phone was in a generic box and not tied to any carrier. While she was in the store, she signed up for Consumer Cellular service to use on the phone. After about six months, she decided to switch to Spectrum wireless. She received a SIM card and inserted it but it indicated the phone was locked. She has called Consumer Cellular multiple times in the past few months and they say they can't unlock the phone because she didn't buy it from them. I called Consumer Cellular with her and again, they say it isn't locked by them. We took the phone to Target and a person at the cell phone desk looked at the receipt and commented that the "phone wasn't rung up correctly." Not sure what that means. It's like she took the phone to the front of the store and bought it like any other items. The rep said it should have been rung up at the cell phone desk at Target. She bought it unlocked so I don't know what difference that would make. She did buy it at the desk and then immediately signed up for consumer cellular. Target suggested calling Apple and finding out what carrier it was locked to. Apple said it "appeared" to be locked to AT&T but AT&T said it was not. My argument to Consumer Cellular is that the phone only works with a consumer cellular SIM card so it can't be locked by another carrier. Spectrum and AT&T SIM cards definitely don't work.

So: Target can't fix the problem, Consumer Cellular says it's not locked by them so they can't unlock it., Apple says it might be locked to AT&T but AT&T says it's not. My friend wants to use another carrier or trade the phone in but she can't because of the lock. Any thoughts?