I tested these kinds of pay for follower services a few years ago. I had 75k twitter followers in less than a week for under $100.

Within three months I had 13k

Within a year I had about 2k

It hovered around there.

On facebook I bought 3k likes for around $30

I still have 1k likes for that page.

Basically, the only reason I have read that you would want to buy followers is that it can help boost your SEO ranking. It will not last long though and I bet the big social media companies start monitoring for it happening to your account/page if they detect abuse.