I lost my phone can anyone tell me what my next step should be?

I lost my phone when I was out last night. I'm pretty sure I'm not going to find it. I"m with att and I was wondering what my next step should be. I'm eligible for an upgrade but can I use that discount if I don't have my phone anymore? Do I need to go to an att store to get a new SIM card and cancel my other phone usage? Will I have to pay full price for a new one? I'm asking all this because I'm sick of having to have my parents do everything for me and stressing them out all the time lol.