Try a different, unedited theme. Your current theme is a mess. If this one gets mysteriously messed up too without you editing it, then you may have been hacked.
why is the footer.php file being modified !!
Because something is modifying it. Perhaps it’s your host. Perhaps you’ve been hacked. Perhaps your permissions are set wrong and allow it to be modified by somebody who keeps messing with you.
We have no way to tell. WordPress doesn’t do this, so something else is.