I have the same issue.
The keyboard layout is already in English (UK). I tried changing it to another layout but it only registers the English (UK).
The @ problem still persists.
Found the correct seting that works for me
Go to Settings>General Management>Language Input>Phyical Keyboard>Tab S3 Book Keyboard Cover
Set Samsung keyboard to English (UK)
Might need to download it but it should then have the keys in the right places :-)
I followed the advice but when I got to the keyboard settings I had to select "English (US) , International style". Sstandard English (UK) or (US) did not give me correct characters for Shift+2 , Shift+3, Shift+", or \.
Now the keyboard behaves like it looks and like my QWERTY PC keyboard.
Interesting, just switched back to "English (US) , International style" and now keyboard gives shift+2 @, shift+3 #, shift+' " whereas "English (UK)" keyboard correctly gives shift+2 ", shift+3 £, shift+' @. This works correctly in Word and Google haven't noticed any problems in any other apps.
My other settings are:
Language "English (United Kingdom)"
Default Keyboard "Samsung Keyboard"
On-screen Keyboard "Samsung Keyboard" is set to "English (UK)"
I posted in this forum because this is where I found the relevant thread for my original issue. I should have (?) mentioned that I am in Australia using a Samsung keyboard bought here. I guess they do have different keyboard mappings for different countries.