Trouble with unrooting Samsung Galaxy S4

[AC Question]

Hi guys I need help,, I tried to un-root my Galaxy S4 GT-I9505 the other day because i wanted the new 5.0 update. I looked up that you can do it with the SuperSU which i had, so I tried to unroot it. When I pressed the unrooting the app closed and it automatically deleted it self. I was waiting but nothing else happened so I restarted the phone. I thought that it worked but i checked for update and it said that i can't connect because the device has been modified. So I decided that i will get the SuperSU again and try again because it is still rooted. When i installed it I couldn't open it because it said ''there is no SU binary installed and SuperSU cannot install it.'' Then I got root checker just to check it. It says ''Sorry! Root access is not properly installed on this device.'' Then I thought that if I delete all the data that would work so yeah, I went recovery boot on my phone and factory reset my phone. Guess what? Right. Didn't work anyway and now I don't know what to do. I can't update my software and I don't have my phone rooted. Which sucks. Yea, also my phone status says ''custom''. Please help me!!