If you are getting notifications from PixelUnlimited, then your Mac is infected with adware. PixelUnlimited is adware for Mac.
PixelUnlimited changes setting in your Mac. First, PixelUnlimited installs a browser extension in your browser. Then, after PixelUnlimited hijacks your browser, it modifies settings in the browser. For example, it changes the default home page, modifies search results, and displays unwanted pop-ups in your browser.