General :: Change The Restrictions To Some Normal Text Files?

I'm trying to change the restrictions to some normal text files and their result is not what is expected.

For example, when I put:

chmod 000 testfile.txt

on a file that is

-rwxrwxrwx,

it instead becomes

-r--r--r--.

It doesn't matter whether I do it with a root or the owner of the file, the result is the same.

Also, putting

chmod u-rwx testfile

results in the file becoming, again,

-r--r--r--.

Also, some doesn't have any effect, such as

chmod o-r testfile.

Even if I do this, the result is the same -rwxrwxrwx.