I use facebook ads and it only have 1 very specific segment so far. It's 20-40 person who works as a marketing / social media admin.

To me, this looks like something that probably ought to be sold B2B and targeted at companies which conduct campaigns on behalf of clients because the value is in replacing their existing tooling. It might work as a 'white label' type service.

Under that premise, the way to sell that sort of service is with regular B2B practices: cold calling, trade shows, industry publications, etc. The targeted demographic from Facebook is not primarily people who are empowered to make strategic business decisions. The decision makers at the media companies are going to be fewer but have much more influence. At the lower end of the employment hierarchy, marketing staff are mostly just trying to keep their job and will be risk adverse (and depending on a new service is a risk).

Good luck.

*person with age between 20-40

In my view for your product 20-40 is too big. What's your conversion rate if I may ask?