VSFTPD - sub-directory restrictions


I’ve configured vsftpd vith virtual users in mysql database and created 5 users: adminuser, userA, userB, userC and userD.
All users have the same local root: „/home/vsftpd/users”.
Adminuser has write access to all sub-directories. The rest of 4 users have read access.
Under „users”, I have created a couple o directoies, lets say dir1, dir2, dir3, etc. After that, under dir1, I have created 4 dirctories: dirA, dirB, dirC, dirD.
The problem is that I have to allow userA, access ONLY dirA; userB access ONLY dirB, etc. So userA should NOT see the contents of dirB, dirC, dirD.
I’ve tried to use „deny_file” directive, to restrict userA to access dirB, dirC and dirD, but no success.

Is there a way to resolve this issue?