About 2 days ago my unlocked S7 Edge started acting really crazy. I'm using my AT&T sim and it just keeps flashing the "LTE" symbol even on wifi and it gets almost no cellular signal (not even one full bar) and speedtest is very poor. At first I thought AT&T might be having issues so I took out my sim and popped it into my Nexus 6. It worked just fine. Full LTE signal strength and speedtest was in the normal (fast) range. Put the sim back in the S7 Edge and same thing. I've reset all the connections to factory default. This is driving me crazy. I just bought this phone from Best Buy at the end of October. Any suggestions?