I can't uninstall and it's driving me insane

I tried to install Avast earlier today, but apparently I had another version installed a few years ago. I’m getting an error. “Avast is already installed, please uninstall the previous version first.” But I cannot for the life of me find any remnant of it. Not in the Library logs or applications folder.

I need to install virus protection to sign into my work account from my mac ASAP and until I get whatever is preventing Avast from reinstalling off my computer, I can’t do that. This is really frustrating. Please, someone, help?

https://forum.avast.com/index.php?board=5.0