Although the word "advertising" and "advertisement" are used interchangeably in one sense, they are fundamentally different. "Advertising" is a gerund (verb-noun), a non-count noun whereas "advertisement" is a concrete noun. "Advertising" means the business or occupation of preparing, publishing and circulating advertisements; printed or broadcast matter that advertizes; advertisements collectively. "Advertisement" is the act of advertizing, a public notice or announcement in a newspaper, magazine, over a radio or on TV or billboard.
I would look at your sentence this way:
When people are purposely made to believe something about a product through lies in advertising/advertisements, (= public notices or announcements in a newspaper, magazine, over a radio or on TV, etc.), it is considered false advertisement/advertizing (=the act or practice of calling public attention to one’s product, service or need). False advertisement/advertising (= advertisements considered as a group) can be found almost everywhere.