iPhone previously unlocked by AT&T but now showing as carrier locked

An unlocked phone can not get relocked. That iPhone was likely never unlocked. It worked on Mint because Mint uses ATT’s network. The response you get now likely means the imei of that phone has been purged from ATT’s database. You need advanced tech support to research the imei. The quickest way to make that happen is to file an FCC or BBB complaint to escalate to corporate.

@sandblaster as far as I can tell, Mint uses the T-Mobile network.  So if this phone sold for ATT,  was used on Mint I don't understand how it could be locked now.

Maybe there was a memory mixup, and it was another phone used on Mint.

@sandblaster & @kevink thank you both.

I am 100% certain this phone was originally AT&T carrier locked and they previously unlocked it (or at least claimed to.)  My understanding is that Mint currently and always has used T-mobile network, and I remember trying a Mint SIM in this phone prior to getting it unlocked (it wouldn't work.)  My Mom switched over to Mint after the unlock, and used it fine for a few months.  She initially tried to trade it in to Apple when she got a new phone (they rejected because she marked it as a 6S Plus when it reality it is a 6 Plus.)  After that it sat idle for a year or so.  I also have a current/active Mint SIM and it will not work in the phone, either.  I'm questioning if the issue is on AT&T or Apple's end; either way I think I'm out of luck and sandblaster's suggestion of FCC/BBB complaint is my only hope.

Thanks again!

Unlocked phones can’t be relocked.  The fact that it was used with Mint would mean that it was not locked to AT&T.  AT&T has no capability to lock a phone that was either previously unlocked, or locked to another carrier.  Either Apple is wrong, or the phone was never used with Mint, only with AT&T and was never unlocked.

@kevink My bad and you are right, Mint has always been on T-Mobile.

@isaiah82 As previously stated, once unlocked, an iphone should not get relocked but you mention an attempt to trade it in to Apple. Was the phone actually sent to Apple and rejected? Perhaps they didn’t send back the same phone.

Thanks again everybody.

@sandblaster  "Was the phone actually sent to Apple and rejected? Perhaps they didn’t send back the same phone." Indeed the phone was physically sent to Apple, rejected, and she opted to have it returned.  My assumption was it was the (exact) same phone, but you make a really valid point; honestly I don't know for sure.  And totally get that once unlocked there's no going back.

Best,

Isaiah

Hello isaiah82, we're here to help with your Device Unlock Request.

 Let's meet in a Direct Message, so that we can take a look at your device unlock request. Please check your Direct Message inbox (it's the chat icon next to the bell icon in the upper right corner of the Forums).

Looking forward to speaking with you.

Carlton, AT&T Community specialist

@isaiah82 If you are sending in a phone for tradein, who thinks to write down the serial number in case it is then rejected and sent back?

If a replacement was sent back due to repair work, they should send ATT updated information for unlocking information.  But in this case, it appears that the policies may have been missed.  Either Apple forgot to check unlock status.  They didn't send the updated serial number to ATT.  Or ATT didn't store the number properly.

radein, who thinks to write down the serial number in case it is then rejected and sent back?

Lol.  I wrote down IMEI of my 2 trade in phones.