I feel your pain. Until quite recently we lived next door to a student house (in fact we had students on either side but the layout of the house meant that we didn't hear the other side so much).
The first couple of years we had quiet neighbours (I think they were postgrads so not so keen on partying). Then we had a group move in who would play loud bass-heavy music two or three evenings a month. At first they made a token show of being apologetic, but they quickly became quite bolshy if I went round to ask them to turn it down. I'm not naturally a complainer, but when I had to go round and ask them to turn it down at 2am on a Wednesday night I'd had enough and got the council noise enforcement people involved. One visit seemed to be enough to get them to shut up, at least for a few months. As they came towards the end of their tenancy they did gradually start up again, and on their last night in the house they had a massive party in their back garden which I'm sure was purely to spite us (unfortunately for them we slept at the front of the house so that was the one time we couldn't hear them).
Then just when we thought we were finally free of the noise the next bunch moved in and were equally as loud. This second group were more willing to turn the music down when we asked (and to begin with were willing to warn us when they were going to be noisy, although that fairly quickly fell by the wayside). However, that in some ways worked out worse as we felt had to cut them a lot of slack to keep them being friendly and cooperative which meant we were suffering in silence a lot.
In the end the only solution for us was to move as there was no way we could know who we would get moving in each academic year.
Unfortunately, unless you've been in the situation yourself you don't quite realise how hellish it is, which is why you haven't had many sympathetic responses here.
In fact I think some of the responses are well wide of the mark for a number of reasons:
a) "It's freshers week". It's pretty rare for students to be party animals for freshers week and then quiet as mice the rest of the time. The fact that they were completely unresponsive to OPs requests to keep the noise down points to them being "party when we feel like it" types.
b) "It's a 21st so it's a one off". Students tend to live with people from the same year group so it's likely that OP has more "one off" 21sts to look forward to.
c) "They're third years so they probably be too busy working". The second group that lived next to use were third years and still had plenty of time to have parties.
My advice, OP, would be to speak to them, suss them out and see if there is a chance of getting any kind of rapport with them where you could convince them to reach some kind of compromise, but start putting in place a plan of action for what you will do if they're not willing to be reasonable. The council may have got rid of its noise officers but it still has a statutory duty to deal with noise complaints so that would be my first port of call.