Notifications customization

I can't find an app to address my problem. I'm missing important calls and messages on my Galaxy S5. Crazy. I need some kind of app to customize my notifications so that this doesn't happen again! I think what would save the day is a way to get the phone to repeat the notification tone at a given interval, say 5 minutes, until I become aware of it and cancel. Sounds like a simple application to me, but I can't find one to do this. Going nuts! (yes, the volume is turned up and sound is switched on!)