I have done an in app purchase by accident amd its cost me £54.99 i have emailed the app and they said they r investigatingbut still mot heardanything and mow i have been billed for it

All purchases are considered final, but you can try contacting iTunes support and see if they will refund or credit you : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

If you don't want to be able to make in-app purchases then you should be able to turn them off on the phone via Settings > General > Restrictions > In-App Purchases 'off'