When I first switched to Skinny in July last year I set my auto topup to be the 25th of the month and the renewal to be the 1st of the month. Since then it has gradually gotten earlier. My topup went on today the 22nd not the 25th and I see the roll over is in 5 days the 27th not what I set it to . Your're starting to look like Vodafone AU that has 28 day month for prepay users
Why the shortening time, surely it should be calender month say the 1st regardless of whether it's a 28 or 31 day month??