Samsung S4 unlocking issue
I had purchased Samsung S4 from ATT in 2013 and got it unlocked almost immediately. I have been using it ever since on ATT and once out of US when on an overseas trip. Then, ATT pushed Android upgrade sometime in 2015 and the phone got locked again. I didn't realize it until couple of days ago when I again traveled internationally.
I contacted ATT through att.com/deviceunlock to have it unlocked, however, my request got denied stating that the device is not on their network for past 6 months. That is untrue. I had my account refilled (prepaid service) in end of April 2016 without any breaks in service in between. There is no way to contact ATT through the website or e-mail to clarify and point out their obvious mistake.
Could someone please help me out of this conundrum. I would sincerely appriciate it.