Push notifications not working even after i've enabled them in 'Settings'

I want Push notifications - alerts, badges, sounds. I accidentally pressed 'Don't Allow' when asked in Instagram and Kik. I read up on the issue and have been advised to go into Settings > Notifications> 'App' and then change the Push Notifications to 'on' but even after i've done that there has been no change and I still dont receive any notifactions when the app is not open.

How do i fix this???? I read somewhere about changing dates to 24 hours after and then re opening the app or something?? I'm not sure how this works. please help me. It's very annoying to be recieving messages and not know that i've gotten them.

Thanks.