Hello back in the year 2014 I promote a Facebook Site with a Campaign, I and invest 120$ I get very fast in the first 20 days over 2400 real Fanpage Likes, but now in the year 2018 you will get maybe 50 Likes for 150$ what Zuck has done here? Has anything changed on Facebook since 14?
Everything has changed since 2014, but you should still be able to get $0.05 Likes. To pay $2.4 per like is very high, so you definitely doing something wrong.
Try to change your creatives, your audience (make a little broader for the start), let Facebook run your ad for a few days to see who is more prone to like your page. Make your changes accordingly.
Whats your niche? try to boost something viral. surely you get more likes and engagement