Q: Dropping calls, Cant use cellular data

Its been a week since i got my Iphone5s and I already browse and done alot of possible solutions for this but seems It couldnt just get fixed with those. My problem here is that whenver I use cellular data and try to use the internet the signal drops from lte to 3g until edge and then itll go no service. I tried reseting the network, Even the restore and any reset thingy but all of those doesnt work. How can I get this fixed? Do I need to visit istore and get this checked? I never drop the unit or watery damaged it. Im actually afraid because i dont have $ to get this repaired. It still has a 1 year waranty tho until march 2017. Can anybody please help me. Sorry newbie here.