Missing visits and exclusion fails

I have latest piwik plugin in Joomla 2.5 on Apache. Opera browser here. I have two issues:

  1. some of visits are not in statistics. My webhoster has Awstats available for the admins, and there are much more IP addresses than in piwik. Any idea what can be the reason?
  2. in the piwik setting I choose the option to exclude my visits. I download the cookie and seems to be OK. Next day it says again, I am not excluded.
    Thanx for help