SIMs are shipped first class and and should take no more than 3 working days to arrive. Please check the address details are correct under your details page here http://www.giffgaff.com/profile/details if your address details are fine and it's been more than a week contact a giffgaff agent to investigate.
To contact a giffgaff agent please go to your My giffgaff page and you'll find links to the Ask an Agent form half way down the left hand side. Here's a https://support2.giffgaff.com/app/ask/Getting-Started/My-SIM-hasnt-arrived/form/ link to it in case you're on a mobile.
Please note as giffgaff agents deal with a great deal of enquires, an agent can take up to 24 hours to answer your question. Any agent replies can be found in the “Messages From Agents“ section here https://giffgaff.com/support/questions
I hope you manage to get the sims delivered using the help above.
You will have to double check your address if correct. Here's a https://support2.giffgaff.com/app/ask/Getting-Started/My-SIM-hasnt-arrived/form/ ask agent
please note as giffgaff agents deal with a great deal of enquires a agent can take up to 24 hours to answer https://giffgaff.com/support/questions