i didnt otherise a payment. how do i get a refund

Did you enter a free trial with an app which would then charge you automatically, or buy a free app which has in-app charges? By doing so you effectively authrorise the payment.

To cancel a subscription please see View, change, or cancel your subscriptions - Apple Support

Strictly speaking all purchases are final (after all, you can't very well return them): please see this page for information on requesting a refund: Request a refund for an App Store or iTunes Store purchase - Apple Support

However Apple have been known to be sympathetic in cases of actual error, so it's possible that they may allow you a refund as a one-off concession: but please be aware that they are under no obligation to do so: go to iTunes Store - Contact Us - Official Apple Support

Alternatively go to the page suggested in the Help page linked to above: Report a Problem