Can't Get Rid of Sophos

I have been trying to install FortiClient on one particular computer, but every time I try, it says Sophos is still on there. I uninstalled Sophos through Programs and Features, I used a script to uninstall it, I searched the C: drive looking for all folders and files, and deleted any Sophos products. I went to the registry and deleted all traces of Sophos, but still FortiClient thinks Sophos is still on the computer. I can't find any trace of it.