App wont connect

Hi all Im new and in trouble with an app, I have installed my networks app (Three) from my new phones ( Moto g) google play store so I can check my credit etc, but when I try and use it, it displays a "no network connection" even though the phone is connected. I have contacted Three, as its their App and their network but so far they have not replied. Can anyone here give me some help please. thanks in anticipation