Past Text Message History Needed

I was told from other people who have done this that I am able to received the history of my text messages. They said they were able to request the texts back to a certain date. I am needing this done for court purposes. Having a print out with the time and date showing that the texts were never altered in any way is what I am needing. How do I go about doing this? I just swapped over to a new service back in Sept. I was under my parent's plan (which they still have with AT&T) and if need be, I can get them to do this for me since I am not a 'verified' person, unless knowing the account password is all I need. I still have the same number now as I did then. Any help would be appreciated.