Volume on iphone 5 not working?

I got my iphone 5 about 3 months ago, I got a update on the iphone maybe a week ago, my phone was working properly till I updated it and maybe a hour after the update I was listen to music, when I tried pressing the down button it didn't want to work, I now have to press it a certain way to work, I haven't dropped it or nothing since I got it. Will AT&T or apple store fix this, I'm not going to pay 100 dollars just to fix something I didn't have to do with. Will AT&T replace my phone or repair? How long will it take, please and thank you

I hate iPhone. I'm using Nokia Lumia 920

Your iPhone is under warranty. Call Apple and see what they'll do. If your iPhone is less than 90 days you'll be given phone support. If not you can get help on the support discussions forums. You can also take it in to an Apple store and they'll fix it. Since you didn't damage it and it's within 1 year of purchase, you're fine. If they can't fix it, they'll give you a new one instead.