My iPhone won't start

Hi, my phone drowned and i need to talk by chat with someone... but i can't get my serial number... and i can't find out how can i search for the answer i'm looking for... i want to ask Apple how much will it cost meto repair my phone... or if i can give them my broken phone as an exchange and give them the difference to buy another iPhone.

I'd like to know if i can do something of that... or how can i contact the Apple support without using the serial number D: