Adding use strict; at the beginning of your script (and fixing everything it subsequently complains about) would likely have pointed you directly at the problem.

According to Net::SFTP::Foreign, $sftp->ls($remote, %opts):

Returns a reference to a list of entries. Every entry is a reference to a hash with three keys: ...

Thus, your

# List remote directory contents
  @$remotefiles=$sftp->ls($remotedir);
[download]

should not have the @ in front of $remotefiles.