@kochaijan If you are leaving giffgaff and wish to take your number to another service provider, you will need to request a PAC (Porting Authorisation Code) from giffgaff in order to give it to your new provider.
Once issued, the PAC is valid for 30 days (after which it expires).
Once you transfer your number out you will permanently lose any remaining giffgaff airtime credit, goodybag and payback points you've accumulated.
Once you've requested your PAC it will sent to you along with its expiry date by SMS within minutes. To see your PAC instantly, go to your My giffgaff dashboard here http://www.giffgaff.com/dashboard and look under your mobile number.
Finally, to avoid any future charges e.g recurring goodybag and/or auto top up please remove any saved debit/credit card or Paypal details under your payment details page here https://giffgaff.com/profile/payment-details