I am sorry to see your problem about the unexpected £ 20.00 payment. Please contact a Giffgaff Agent regarding your account related issue, they will be happy to assist you with your enquiry.
Giffgaff Agents are the only people who can authorise refunds @jeann14, when appropriate. Giffgaff Agents usually respond to your enquiry within 24 hours and can be contacted here (Contact an Agent)
Agent replies can be accessed through your My Giffgaff (AKA Dashboard), or directly in your Questions (Agent Replies) area.
Please take time to navigate to your Giffgaff Payment Options and ensure that Recurring Goodybag and Auto Top-up features are OFF (disabled), if not required Link: Giffgaff Payment Details. If one of those features is enabled, this may be the reason for the £ 20.00 payment.