Goodbags last for a calendar month. February has 28 days, Doesn't matter if you buy it on the 1st or the 27th, you will get 28 days. The one that you buy in March will have 31 days.
I've just topped up today. February 11th. I have bin given 27 days aswell. How the hell does that work out????
Goodybags last a calendar month, February has 28 days.
Next month March has 31 days, you'll then have 31 days for your goodybag