If you've never been sick, then how do you know the process? How do you know that it's not like when you have something like a virus and you simply call out every day for 4 days like the doctor says and bring the note in later? If you haven't been through an extended sick period, how do you know the difference?
I've been on FMLA three times with two different workplaces. Each time was different, even when I was still at the same workplace. Every time was different. And that's with me knowing what to do with extended absences. FMLA leave #2 and #3 were the employer telling me to take it. Even though I know the legal procedure, I just didn't see how my current issues were such that I should take it. The last time I was a part-time worker and I thought that part-time workers were not given FMLA protection, so I'm glad my employer said take it.
So blaming the OP is just wrong all the way around. Even if he's been calling out every day, seeing how it's related to an on the job injury, HR should have been proactive in telling him to take a LOA and how to do that. Especially since for some weird reason Target doesn't call FMLA that, it calls FMLA an LOA, and that bit of terminology difference means to the average person that one is totally different from the other. I had absolutely no clue that the LOA I was told to take was FMLA until the doctor paperwork showed up. Sorry, if HR hasn't been explaining to the OP long before now what his best course of action is, then HR is the one being adversarial and has actually been withholding information that the OP needs in order to know what to do. Probably because workman's comp claims make your workman's comp insurance rates go up.