Hi @harini
Thanks for the detailed description of the issue.
I believe the the solution is quite simple, and is the fact that you care using the wrong $post_id parameter to load data from a taxonomy term.
Please read over this article and pay special attention to the post_id param:
http://www.advancedcustomfields.com/resources/how-to/how-to-get-values-from-a-taxonomy-term/
Your post_id param should be
'category_' . $category_id