Are you on dedicated server ? if yes, login to WHM as root, check in Feature Manager stats are enabled, also in Server Configuration > Statistics Software Configuration & Tweak Settings If you are on shared hosting, you need to contect your web host.
With reseller plan, you have no control over enabling or disabling stats. Awstats button is missing in cpanel ? All sites use same skin ? If skin is different, it can be disabled in skin. Its better ask web host and see if they disabled stats for these sites.
It could be that the manager of the server has setup so that the logs are deleted, which would stop awstats from updating. You'll need to contact the person that run the server.