If you are getting notifications from GigaPromo, then your Mac is infected with adware. GigaPromo is adware for Mac.
GigaPromo changes setting in your Mac. First, GigaPromo installs a browser extension in your browser. Then, after GigaPromo 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.