Sprint unlocked Galaxy S6 says invalid SIM when an AT&t chip put in
Sprint unlocked my galaxy S6 for me and I took it to AT&T and when they put in chip it said INVALID SIM CARD. The at&t representative tells me it is therefore not unlocked. I call Sprint, they tell me it is unlocked and that it has something to do with technical stuff on AT&T's end. I do all the system updates, factory reset and take it back to AT&T again still not working. I call Sprint again and they say the galaxy s6 was automatically unlocked a while ago as soon as my mom had upgraded her phone and paid off the galaxy phone. So even though I went through the process of requesting them to unlock it and the lady told me it would take 48 hours for it to be unlocked, apparently it was already unlocked this whole time, per a very curt Sprint representative. The Sprint guy also said it was no longer sprints problem and that again at&t had to do some technical stuff on their end in order for it to work. I've gone back and forth so many times from Sprint to at&t. At&t keeps telling me it is locked. Sprint says unlocked. Help please, I don't want to give up on this and I refuse to believe that it's just not compatible on the at&t network because I've seen other people have success from doing the Sprint to at&t thing with a galaxy s6.