Well, if MalwareBytes didn’t find it, you can always keep looking with something else. I wrote a little diagnostic program to help show what adware is installed. Download EtreCheckPro from https://www.etrecheck.com and run it. Create a new reply and use the "Notes" tool below to add your EtreCheck report.
If adware is installed, EtreCheckPro will help you remove it, although you may have to supply a password. If you aren’t comfortable with that, just post the EtreCheck report here and other helpers can tell you exactly what files need to be deleted and how to do so.
Disclaimer: EtreCheckPro is my own app. EtreCheckPro is free to use but has in-app purchases available. Downloading EtreCheckPro or using it could give me some form of compensation, financial or otherwise.