I can’t unlock a phone from the network

You bought a second-hand phone and didn't ask if it was unlocked?  Given that level of attention to detail, 

I have checked its eligibility and everything looks good to me

means very little.  You don't even know what kind of account it was on, so you don't know if it was on a PREPAID account for at least 6 months, or a Postpaid account for 60 days.  You don't know if there's a balance due on the phone, etc.

I knew it was on AT&T and I have unlocked other AT&T phones before but this this is the first problem I have encountered so far

Hey there @milesa1221,

We understand, and would like to point you in the right direction.

The Community Forums are a public support option where other users, and AT&T, will try and assist with high level support needs. This means we won’t be able to look into account specific concerns. To get the help you need for your unique issue, please review our Contact us : https://www.att.com/support/contact-us/, and choose the best option to reach out to us. You can call, chat, or reach out via social media, and we can review your specific issue and provide you support. If you feel your issue isn’t account specific, and can be answered generally, please let us know, and we’ll be happy to help.

Thank you for visiting the AT&T Community Forums.

Andrew, Community Forums Specialist.

I tried that and it didn’t help so I went to forums.

No one on the forums can unlock a phone.  Only AT&T can do it, and the proper way is through the online unlocking portal.  Are you trying the unlock as a customer or non-customer (answer no to the question of whether you have an AT&T phone number)?  The only information required for a non-customer is the IMEI.

I came to forums seeking help. When I did the unlock I put in the imei and they emailed me saying to call them and then I got stuck in the loop. I just need a person to help me with this process 😭

AT&T doesn’t do direct customer service through the forums.  They won’t contact you.  All they tell you to do is to contact them using the contact link as in the message from Andrew.  You can try filing a BBB or FCC complaint to get the issue escalated to upper management.

Ok. I’ll try that.