Unfortunately, unlike other mobile providers giffgaff do not have a customer service department or telephone number you can ring to speak to a person. All the support is done online.
However, if you have query that is account or billing related you can get in touch with a giffgaff agent
To get in contact with a giffgaff agent please follow this https://giffgaff.com/support/questions
Or If you have a technical issue, you can post it on the community here and members will try to assist you.