unable to root

I have a samsung galaxy s4 Verzion (Sch-I545) and it is currently running on android lollipop 5.0.1. And I have found that i am unable to root it for some reasons. I have tried to to root it using kingo root ( 3 times) , using king root ( 2 times each using different versions) and using towel root. However all attempts failed. I would appreciate any help and useful information on my issue. Thanks.

Sent from my SCH-I545 using Tapatalk