Suddenly showed up on my credit report

I have no idea who these people are and seeing all the comments I am scared to try and contact them. I have been keeping an eye on my credit report for the past 6 months and call my debt collectors to try and figure out who they are coming at me for. Then suddenly out of the blue this company shows up on my credit report for $515.00 I do not know who this company is as no one has ever tried to contact me nor do I know any one I owe money for that amount. Don't they have to try contacting you before they post it to your credit report?