can't download apps on cydia with wifi

[bender o]

Hi, i have an strange issue when downloading apps over wifi from cydia, when i'm connected to wifi i can navigate and use safari as usual, but when i try to use cydia it says that it has timed out and won't download, but when i use 3G it works perfectly (but i'm a couple of megas from going over my limit so i'm stucked).
What can i do?
Thanks.