Boys at school are mean :(

What on earth, that seems so unprovoked? Are there like no girls at the school or something, might explain why they're acting so ignorant.

They have been for a while. I wish I was back at my old all girl's school. Anyways, this isn't a vent lol.
Here's the issue:
When I say something they laugh and giggle, like I cannot hear them.
One let me leave through the door first, I thanked him, and he silently, to himself, told me to Shut up.
When I answer my questions in class, they murmur. And when they sit near me, they make a comment.

I don't know what to do, and it is bothering me so much. I'm in year 13. I thought everyone would be a lil' more mature.

Sorry to hear about this, when people are so bored of their own lives they enjoy pestering others to stir up trouble. You're in yr13, so it's not going to go on for much longer, though it would be worth not talking to them at all - ignore them completely, don't talk to them and don't even thank them for anything - they don't deserve it. Another solution would be to sit further away from them in class, so they can't get to you. Lastly, it would be worth speaking to your teachers privately regarding their behaviour and the laughing thing, so that the teacher is aware and can shut them up whenever they do it. A lot of people do get mature at this age, though not all of them do unfortunately and this was common in my sixth form too.

I hope things improve for you