I have a website with an integrated Web service (an app for card divination online). Age of domain is already almost 2 years. Naturally, I wanted to make my site popular. First I submit my app in the link directory. And the effect was good. But then I mistakenly ordered the services from one 'SEO expert'. He just spammed my site for blogs, forums, etc. As a result, now the site has only 20-30 visitors per day. It is very little for a unique resource.
Perhaps Google specifically lowers the SERPs for my site. How is it possible to check and how to get rid of this?
I think you have to work on your SEO. It will take time: few weeks to several months. Your market (fortune telling I understand) is, I think, quite competitive because it's a big market (based on the volume of search, from Google Adwords Keyword Data).
I recommend studying keywords, search volume, and competition for the given searched keywords.
There is a great video here about the SEO tool Market Samurai: http://www.smartpassiveincome.com/webinar-replay-100623/ This blog has lots of advice on how to get more traffic, and the blogger shares interesting data about his revenues.