Switching on Push notifications on an app?

Dear All, I am posting questions with increasing regularity but simply because I seem to be getting more than usual problems. This one is regarding push notifications on an app. I downloaded VIBA on Sunday. This is a WI FI telephone and e-mail client which a lot of my friends have got and I just wanted to see if it was accessible with voice over. When I downloaded the app I missed the question that asked if I wanted to activate push notifications and by mistake said no. The next page in the app set up said that you need to have push notifications on to use the app and provided instructions of how to switch these on in settings i.e. go to notifications, VIBA and switch on notifications, which I did. I went back to the app but it still thought I hadn't switched notifications on. I then deleted the app and re-installed it and it still didn't work. I then went to I Tunes and de-ticked the VIBA box, reloaded it and the problem was still there. What can I do? Do I need to turn the I phone off after switching on notifications? However, I guess I could do it by deleting the app all together from I Tunes but I don't know how to do it. Can someone help please? Kind regards, Steve.