Not previous data usage no, your last
Months usage appears on your giffgaff home page on or around the 5th of each month.
Alternatively, you can sign up to recieve a monthly statement email, it would be displayed there for future months.
To receive this email you must 'opt in' to receiving marketing messages. You can do that by heading here : https://giffgaff.com/profile/details
Then change Your contact permissions:
The only box you need to tick is 'Give me info and offers about giffgaff'
Follow this link for all info included in This email AND how to receive it - http://community.giffgaff.com/t5/Help-Ask-the-community-got-stuck/Personalised-usage-statement/ta-p/3522399