Whether or not you pay for something such as Facebook is not relevant to whether or not you are a product.
What makes you the product is if Facebook is making money from you other than any payments you may give. And they are. They make money with the information about your likes, your dislikes, the ads you hover over, the ads you click on, your friends, your games… the list goes on and on. In many ways, facebook, google, and their ilk literally know more about you than your mother. Such as your sexual preferences, your diseases, etc.
All of this information has become a multi-billion dollar industry (Facebook made $18B in 2016, google somewhere around $60B from ad revenue alone).
If these companies had zero information about you to sell to advertisers, your value would be significantly diminished. Perhaps to zero.