Well, if you have gone with a dodgy black-hat SEO company then the answer is probably yes! To determine whether your site has been banned in Google, a simple and easy technique is to insert “site:domain.com” into Google and see whether any results come up. If not, then you should probably sign-up on sign-in to Google Webmaster Tools and see whether your domain has a specific message from Google highlighting that you have been banned.
There are also a number of SEO tools that specifically look to see whether you have been banned from search engines. If you are not banned, then there is clearly another problem into why your website is not getting indexed. It might be wise to speak to an SEO consultancy that might offer to fix the problem for free, or a small cost. It could be something as simple as you are blocking your entire website in your robots.txt file.