Question? – FooCall | Cheap Calls Review

I just got this app because was recommended from a relative. I tried to do my my first free call but not talking with anybody and I added money for futures calls. In the screen appeared a question if I want to top up or not now. I choose "not now" and now I'm not abel to do anything. I have the screen in black . Can someone help me, please. What I need to do?
Review by S0039 on FooCall | Cheap Calls.