Last few weeks I purchased an app and today i tried to update my app as uual including instagram (which supposedly neednt to pay like others), but it stated i have billing problem with my previous purchase. I dont get it. help?

You may need to update your billing information > Pay an unpaid balance in the i Tunes Store

I was charged online for something that I don't remember I purchased so I didn't pay it. How do I correct this if it is my error? I need to know what the charge was for.

Sylvia McClain

To see what you owe (and what it's for) : Pay an unpaid balance in the iTunes Store - Apple Support

How do I cancel the renewal of an app that i no longer want to use?

There are instructions on this page for managing and stopping iTunes auto-renewing subscriptions : View, change, or cancel your subscriptions - Apple Support