To be fair to Sky I don't think it's a problem with their app. It updates for me properly each time so I imagine the problem is with your PC or laptop.
When you uninstall it and then delete the folders, which folders do you delete? There are some in appdata local, locallow and roaming. There are some cisco folders that could be deleted when uninstalling that may help too.
There's a guide somewhere on how to properly uninstall it all. I'll go get a link.