The operating system on your devices has been modified in an unauthorised way.

Can someone help me?
I rooted my Samsung Galaxy Mega 2 to play Pokemon GO using fake GPS. I root it using KINGO ROOT. But after a while I unrooted it using the same app and everything seems normal. But oneday my camera app failed and after doing some research, I must upgrade my latest phone softaware.
But everytime I check for updates, an error message appear. Here's the message:

The operating system on your devices has been modified in an
unauthorised way. Try donwloading software updates using Samsung Kies
on your PC or visit a customer service centre.

What should I do?
I already use Samsung Kies but I think it didn't worked.
Need help!
Thank you!