Sorry to hear your experience was crappy. Hope you are able to resolve this.
Although I have always done an in-person trade in the past (Apple Store or AT&T), I went ahead and sent my iPhone 11 in via the UPS package Apple sent. I received an email within 24-48 hours indicating "Your trade in is a success!".
Sounds like I lucked out.
I must admit, if I had seen a forum such as this before I mailed it, I would likely have traded it in in person.
Best of luck, keep us posted...
Nice, glad yours was accepted. I also traded in my wife’s 12 mini and that went through without an issue.