I flashed stock firmware on my s5 and my imei has changed. sim card wont detect.PLS HELP

[AC Question]

so i recently got myself samsung s5 sm-g900f and battery life was terrible so i decide to flash custom roms and all but it didnt help , so i tried to flash stock marshmallow on it but odin kept failing , i tried 5 different sm-g900f firmwares but none worked however i noticed when i use to keep my phone in download it use to show product name sm-g900p so i gave it a try coz my phone had got soft bricked , sm-g900f firmware worked perfectly without errors and my phone booted up but i noticed my imei doesnt match with the one on the back of my phone..i took a efs backup using this app but its not restoring it back either..my phone shows my carrier app but i dont wht it doesnt detect it..pls help