Worst customer service experience ever

So I'm in the midst of the most frustrating cell phone experience of my life.  I paid off my s23 ultra 2 years ago.  Ordered the s25 ultra.  Upon receiving it I was told the s23 ultra was unlocked.  I sold it to my neighbor. It was not unlocked.  Now the s23 ultra is showing on my account that I owe full payments instead of the s25 ultra.  The s25 ultra has been messed up by xfinity and can't be used. I've never raised my voice with any xfinity employee or misbehaved. But after over 3 weeks and over 100hrs of being on the phone with xfinity, being disconnected and having to start from the beginning over and over. I'm very frustrated. Having to buy back the s23 ultra was an inconvenience as well. Nobody has been able to activate the s25 ultra and I'm having to use the s23 ultra and pay for it again is unacceptable.