Pretty sure that they can't do that, especially given the notice given. May depend on your award/agreement etc. Tbh it's none of their bl**dy business why you need the day off!! What if it was for a specialist Appt? Where's the list of approved reasons!?
Lol, sorry bit ranty there! I used to do rostering for a big business when I was 20/21/22 yrs old and we had a mostly causal roster base. As long as the leave request was in with plenty of time the managers could do FA! I loved seeing what others wrote - going to big day out, stereosonic etc and nothing they could do! However if ppl continually asked for every Sunday off for example then I was instructed to give them less hours on draft rosters.
I think if you'd asked once the roster was out then they can say no but sounds like you haven't don't that. Hate the honesty can sometimes back fire