If your WordPress feeds don’t seem to be updating but remain “stuck” in the past (this can happen particularly after a migration of a site to a new server), enter this snippet into the functions.php file of your theme in WordPress:
add_filter('wp_feed_cache_transient_lifetime', create_function('', 'return 60;'));
Once this is in place, visit your feed URL in a web browser, then wait (literally) a minute for your RSS feed to update and it should begin working normally.
Once you have confirmed that the feed is working, comment out the above line in order to return to the default 12 hours update cycle or replace the value of 60 seconds with something more reasonable so as not to overburden your server with RSS updates.