I changed from 60GB to 150GB naked cable after the price drop. 
Opened the bill today and I have been charged the old ($155) 150GB price not the new ($95) price.
Rang Vodafone, yes it is a Sunday. About a 5 minute wait (it is Sunday) and all fixed in 5 minutes.
Thanks Vodafone, you made an error, getting it fixed was easy.