Phone marked as stolen and it's not

Whatever you think the problem is, it's not that. 🤦🏼‍♀️ 

Return the phone! 

they think the phone I am still paying off is linked to his sim card and if that sim card was installed into another device that would look like I'm trying to break contract.

No they (At&t) don't, and AT&T doesn't care if you swap sim cards and buy your own replacement phone. People do it all the time. I did it. 

Since you don't have a contract, and customers can replace phones with a bring-your-own-device at any time they choose, that is not what the problem is. The problem is the new phone, it is the one that is blacklisted.  It has absolutely nothing to do with you. You were sold a blacklisted phone, which was blacklisted before they sold it to you. 

    Contact back market and let them know that they sold you a phone that is showing up as lost or stolen. You can look this up yourself by the IMEI.

By the way AT&T cannot Blacklist a phone that they did not sell.  AT&T does not blacklist for non-payment. And you have done nothing wrong that would cause AT & T to Blacklist your phone or a phone that you purchased from outside of a t & t. 

 AT&T has absolutely nothing to do with the phone being blacklisted , other than enforcing the universal blacklist which was begun by whoever reported the original IMEI of your replacement phone as lost or stolen.

Once you replace the phone with one that is not defective, not broken, not blacklisted, and one that will work with AT&T LTE only Network, you have to contact a t and t and have his line restored.

    If you're purchasing an unlocked phone, please make sure it is a North American model listed here. After the 3-g shut off not every phone is capable of voice over LTE and would be excluded from the network

Non-carrier branded phones that will work on AT&T now that 3-g is gone

I bought him a cell phone outside of ATT

@Meglyons3 Where did you buy your son's phone from?

Back market. 

@Meglyons3

Back market.

???

It's a reputable online storefront for refurbished devices 

The original owner reported it. You bought it 3rd party and it doesn’t matter how reputable you think the company is. Return the phone and get a refund. 

@Meglyons3

It's a reputable online storefront for refurbished devices

Then you shouldn't have any problem getting your money back.

Time to return it.

They marked my son's broken phone as stolen. Not the new one

@Meglyons3

They marked my son's broken phone as stolen. Not the new one

After you removed the SIM from your son's old broken phone, and placed it in the refurbished phone, then it marked your son's old broken phone as stolen?  And refused to make the refurbished phone work.

That seems very strange...

Correct.

And as I stated before,

When I upgraded my phone two years ago the manager massively messed up my plan and "cross upgraded" (the words they told me) and my phone that I'm paying off is reflecting on both of our numbers on my account and the next plan is assigned to his number! ...... Which would make sense if they flagged it as stolen, they think the phone I am still paying off is linked to his sim card and if that sim card was installed into another device that would look like I'm trying to break contract.

I've tried to get them to fix this and they told me there's nothing that can be done until my phone is paid off. So basically I'm stuck with whatever casualties happen with my son's device ?