mobile

I am facing a weird issue with HTC One E8 slot 1 . No china unicom sim works in slot 1 of e8 . After few second an error pops up "Network or sim error" . On slot 2 the sim works fine on 2g .

Slot 1 was working perfectly fine with 3g when i left india . How can i disable 4g mode on this phone . I tried with 2 different 128k sims of china unicom . Is that a result because the phone cant change 4g to 3g or disable 4g completely