(English is not my native language; sorry if 당신 find misspellings).
I'm not sure.. But I think the 4th season is just a rumor T-T
I searched in many websites... And I think it's all false. Between the seasons, there's just 1 월 of break (I'm not sure if I'm saying this right, but I think you're understanding what I mean.. if 당신 didn't understand, I'll try to write in another way ^_^). The last episode aired on March 26, 2010 - And now is 2012. So.. I think there's no 4th season ;'(
But if 당신 really want a fourth season, sign this petition:
link I already signed - I think 당신 should sign too :D
And if 당신 didn't like the ending in the anime, 당신 should read the manga. The ending is waaaaay better. I think you're going to like it *-*
Hope it helps =]