Unlock code on Samsung j3 not working, now I am locked in ATT network

I have exactly the same issue with AT&T and no-one has responded to my inquiries in the past few days.  If you find a resolution, please post and let others know too.  Thank you,

I spoke to Samsung; they say that they have no control over the lock on the phone. It's ALL ATT's doing; they lock the phone, and they make the decision to lock the phone to ATT permanently after 5 attempts. So right now, my only option is to have the phone unlocked by other means without ATT even knowing about it. 

I can't even understand how this is legal; just unlock my phone! 

Here's the latest situation  ( I will be using PG-13 foul language, similar to Good Place series):

I have paid off the outstanding balance on my phone, and my phone is eligible for unlocking. I formally requested the unlock code through website, and on the phone. I have been given an unlock code for the IMEI number that I have provided. I have tried this mother forking code many times with a non AT&T simcard; it did not work. I have contacted Samsung with this issue, and they told me that the lock is completely software related, and they have no control over this, it's all AT&T. So I called in AT&T for the 8th forking time, and I finally got someone who is marginally more competent, and I got my hopes up that maybe this time it will be resolved. I told them that I am getting "SIM network PIN blocked. Enter SIM network PUK." with my non AT&T sim card, and the only reason why I am getting this message is because the unlock code AT&T has provided did not work for 5 consecutive attempts. 

Right now, my phone is locked to AT&T network for eternity, and these idioms are telling me that there is absolutely nothing they can/will do to make amends. I fully paid my phone but  my phone is locked and can only be used with AT&T, and I cannot use my non AT&T simcard or any other simcard with this phone, and there is nothing I can do about it.

If you think I will not take action against what you're putting me through, you're gravely mistaken. I will find a way to unlock that phone, don't you worry about that. I will also file a formal complaint with the Massachusetts Attorney General and explain to them how much shot you have put me through just to get my forking phone unlocked to be used for an overseas travel. I will do everything in my power to make sure that people hear about your idiomic policies and I will recommend everyone I know to stay away from AT&T unless you want to be treated like scum. Oh, needless to say, as soon as I get this phone unlocked, AT&T and I are done.

 I was given an unlock code several times by AT&T under the Sim block also

https://www.google.com/url?sa=t&source=web&rct=j&url=https://consumercomplaints.fcc.gov/hc/en-us&ved=2ahUKEwjv7-CMnp7kAhVVoFsKHT2pAKEQjBAwAXoECAYQCg&usg=AOvVaw04fbc5423Io-dm1mXJnOuY&cshid=1566743460505

customers may request that the phone be unlocked so long as the device has been paid in full, and the account in question is not past due.

Notice. Carriers that lock devices will clearly notify customers that their devices are eligible for unlocking at the time when their devices are eligible for unlocking or automatically unlock devices remotely when devices are eligible for unlocking, without additional fee.

Disclosure. Each carrier will post on its website its clear, concise, and readily accessible policy on mobile wireless device unlocking.

Just an FYI. The OP was being asked for the PUK number. Not the phones unlock code.  A PUK lock looks a SIM card to a particular phone.  It prevent someone from stealing your SIM card and using your plan.  Has nothing to do with a carrier lock on the phone.  

I have the same problem, my Samsung J3 is not unlocking when unlock code is entered. It keeps saying "invalid unlock code". Even though this code was provided to me by AT&T themselves. When contacted several times, AT&T keep blaming Samsung for the problem and are not willing to cooperate further to resolve the situation. I am very upset with AT&T and I am never buying an AT&T phone or service again. 

Steps that have been tried so far:

-Format entire phone and hard reset done.

- Updated phone to latest software firmware done.

- Phone has never been rooted or tampered with.

- The unlock code provided by ATT unlock device portal has been tried 9 times so far with no success.

- AT&T not cooperating and are not helpful.

Please folks, if you have found a solution to this unlock problem, please share. I truly appreciate it. Thanks.