Give them a ring. Tax people are actually quite helpful. I know the form you mean as I�m self-employed as well. It�s a form you can do if your turnover is below a certain value or your income is not complicated. Obviously your student loan does make things a bit more complicated so my guess is they missed it last year.
The good news is the full form is not that difficult. I�d recommend you do this ASAP and you can download what you need from their website. There is a backlog of forms to process at the Revenue and if yours isn�t processed in time you�ll find yourself guessing at how much to pay on 31 Jan. I�m sure you know this, but if you get it to them before the end of September each year you won�t have to do the calculation yourself, which is nice.