G.I. Bill question

When I first enlisted my recruiter told me that I didn't have to pay into the G.I Bill until I got to basic. When I had arrived at basic they told me it was too late to start paying into it. Once I got to my first until I was told I am sol. It's been a few years and it's been gnawing at me since basic. Is there anything I can do to pay into my G.I Bill now or is it too late?