please help me

hi guys

I bought glaxay s 6 before couple days

it was 5.0.2 lolipop

i tried to update it but it appear a strange message says :
“The operating system on your device has been modified in an unauthorized way. Try downloading software updates using Smart Switch on your computer or visit a customer service center.”

i didn't know what to do and how to fix this

i asked some people and the tell me to download the framware from sammobile

i downloaded the ksa 5.1.1 framware from sammbile and i installed using odin

after the install end the phone didn't work and it stucks on the samsung slogan

i tried to open the download mode and make wipe data and wipe cach but still didn't work

i try another framware and make every thing

but the phone still stuck on the samasung slogan

i want to your help guys

thanks