Sorry to read that you're unable to log into TV Anywhere on your Samsung Galaxy Tab S2.
I've checked for any issues with TV Anywhere and it is showing as fine. Is this now working for you?
When signing in make sure that you type it in manually rather than using auto-fill as sometimes it can add an extra space at the beginning of the username or at the end. Even though you can sign into your Virgin Media, have you tried to change the password to see if that works?