(English is not my native language; sorry if te 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 mese of break (I'm not sure if I'm saying this right, but I think you're understanding what I mean.. if te 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 te really want a fourth season, sign this petition:
link I already signed - I think te should sign too :D
And if te didn't like the ending in the anime, te should read the manga. The ending is waaaaay better. I think you're going to like it *-*
Hope it helps =]