Why I can't change my network type on Android Kitkat ?

[AC Question]

I tried to change my network type from EDGE to 3G but I can't access "Preferred network type" in Settings it's always showing as a blank text, Mobile Data is always on EDGE although both my phone and my provider supports 3G , I tried to dial *#*#4636#*#* code but it didn't work too
Any one has a solution?