How do I find out if I filed as a dependent for my parents? They cannot claim me as usual

It depends.  If you no longer qualify as your parents' dependent, you would first file as an independent.  If your return is accepted, then you know that they have not claimed you.  If your return is rejected, then it is likely that they have claimed you.  

Before you do, however, you may want to click on the following link to learn more about what is a Qualifying Child.  The two things that will affect you the most:  your age and whether you provided at least half of your own support.  If you are under 19, or under 24 and a college student, your parents can claim you if you did not provide at least half of your own support.  However, if you were at least 19 and no longer a student, or at least 24, and earned more than $4050, your parents could not have claimed you under any circumstances.

If you provided at least half of your own support, please comment your situation and I'll be happy to provide additional information.