Welcome to TPG Community!
What device did you use to access your "My Account" page? Did you use a computer or just the mobile phone?
If you've used the mobile phone to access the website before and was not able to see the button, please try to use a computer as it may be visible there.
If it's still not working, please let us know.
We can see based on the latest log on the file you have been in contact with one of our Mobile Specialists and processed the activation. Please be advised SIM activation may take 1-2 working days. Let us know how should you require further assistance.