assigning permissions to user-groups?

Hello,

I want to set up different user groups so that they have access to their respective dam assets folders.

i've created 2 groups group A and Group B and asset folders folder1 and folder2.

Now i created users and made them member of group A, they were still able to see folder2(i have already modified the properties for folder 2 and set CUG as groupB).

To each user that I create there were 2 more groups assigned - contributors and everyone , when i removed contributors group assigned from my user, now when i log in with that user it has no access to dam page....I get 404 error.

I want users from group A to only see folder1 and groupB-folder2, How do i achieve it??

moreover how do i do all of it programmatically?

Thanks in advance.