What do interviewers at call centers expect from applicants during final interview?

You could be doing all the right things but perhaps they thought someone else would be a better fit. Don't agonize about rejections as there is an over abundance of educated and experience people currently unemployed and competing with you for the limited openings. It doesn't mean you were not qualified or that you didn't interview well, they just chose another similarly qualified candidate. Just keep doing what you are and you will find a good job.