If it still shows activation in progress when you've logged in you'll need to click the link at the bottom of this page which explains the activation process https://giffgaff.com/support/sim-and-number/activate-your-sim to raise a ticket with an agent as neither myself nor any of the other posters here (apart from perhaps the Educators) have access to your account.
Texting settings to 2020 won't achieve anything on a non active SIM as all it does is request settings for services such as multimedia messaging and browsing.
Season's Greetings to you and I hope your problem is resolved swiftly.
how do i contact an agent?
To contact an agent about your failed activation, head to https://giffgaff.com/support/ask/activations
The agents will reply within 24 hours
Hope this gets fixed soon and sorry bout the delayed activation
Once again welcome to giffgaff and have a merry christmas