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Being just a user like you, I'm winging it here, but look in /Library/Caches/com.sophos.sau/CID. In that folder is Sophos Anti-Virus Home Edition.app, which looks suspiciously like the Remove Sophos Anti-Virus.app that gets installed in the Applications folder when Sophos AV version 9 is installed. If nobody else steps in here to correct or confirm this, and at your own risk, you might try running that to see if it will uninstall the bits and pieces of Sophos you still have.
Being just a user like you, I'm winging it here, but look in /Library/Caches/com.sophos.sau/CID. In that folder is Sophos Anti-Virus Home Edition.app, which looks suspiciously like the Remove Sophos Anti-Virus.app that gets installed in the Applications folder when Sophos AV version 9 is installed. If nobody else steps in here to correct or confirm this, and at your own risk, you might try running that to see if it will uninstall the bits and pieces of Sophos you still have.