Contact an agent and they will help you mate
No they won't. This isn't something that agents are able to help with.
The rules of the Maestro scheme (established by the banks that issue Maestro cards) state that recurring transactions are not permitted against Maestro cards. So if you want to use one, you can use it for purchasing goodybags and credit on a one-off basis. You'll need a different type of card, such as MasterCard or Visa (credit or debit), to recur a goodybag or make other recurring payments. Unfortunately giffgaff isn't in a position to change or make exceptions to those rules.
Very few banks issue Maestro cards any more (the only major ones I'm aware of in the UK are Clydesdale and Danske) so it may be easier to apply for an account at another bank that gives a Visa debit card.