On brother's account. Want to change provider for cost savings. Brother hasn't responded to texts & voice mails. What do I do?2

I am on my brother's account & want to move my service to a 55+ account with a different carrier. I have called & texted my brother on numerous occasions over the past month. I purchased a new phone &, since my brother will not for whatever reason give me his passcode, he has basically hijacked my cell service. I am unable to send in my iPhone XR that is currently on the AT&T account back to Apple for trade in. This phone will no longer be in use & I need to port my current number to a different carrier. I have had this number for over 24 years so surely you can understand why I want to keep the number. I have contacted AT&T numerous times as well to help in getting my number ported over. You can look back at the history of my number & will see the account was in my name from 1998 to 2012. The company I worked for at the time ported my number to their business account because they were paying my bill. When I left in 2015, the number was ported back to me &, unfortunately I allowed my brother to talk me in to getting on his account. Now, I am able to get on a 55+ account & my brother refuses to respond to my texts & voice mails asking him to give me a transfer PIN to port my number to another provider in order to save money. I am on disability &, I can save $35/month going with this new carrier. $35 may not seem like a lot but, when you are on disability, it is a lot. I have explained this to everyoneI have spoken with at AT&T to no avail. Like I said, I have repeatedly tried contacting my brother & he has not responded. I am stuck between a rock & a hard place with seemingly no way out. Any suggestions other than contacting my brother would be greatly appreciated. I have no idea why he is not responding to me, however he is choosing to ignore me.