It takes 8,250,000 to get from Level 20 to 30, according to DDOWiki
The stone gives 4,000,000 XP, which would land you at where you landed, which is level 25 + 2 ranks
30% pot makes that 5,200,000 XP, which would have landed you 50,000 short of 27
You clearly didn't have an XP pot on when you...