I've used the free version of CCleaner for years. After most recent update I didn't unclick the "install Avast" button in time and ended up with Avast installed on my computer. Didn't want it so I uninstalled it with IObit Unistaller, which supposedly will clean up all traces. A week later I still have quite a few Avast files in various places that I am unable to get rid of because my computer tells me they are "in use". I wish for only one thing: T that I could get rid of all the Avast files that even a good uninstaller cannot touch. This is just a rant......
Try this. Make sure you are in safe mode.
Try reinstalling CCLeaner with the Avast, then Use the Uninstall of CCLeaner/Avast, as they will know better to what registry keys, and folders they place on your system, when removing, compared to a 3rd party application staying up to date with CCleaner/Avast most recent system installation settings, and what to remove.
Keep in mind, many programs dont clean themselves up as good as they install.
So its not guaranteed, but worth the try.
You can still run your uninstaller afterwards.