I can't change my galaxy j3 prime 2017 mobile network type from Edge

[Bmd MOSES]

when I try to change through settings,mobile network,mobile networks mode.they tell me that,that setting turns of 2g,some apps may not work where there is no LET or 3g.and all network turns off immediately. but I am sure that at least 3g is there because when I change my simcard to another phone I can access 3g.