slow 3g upload speed

Hi friends,
I'm new at this forum.

Let me tell my problem.
For the last two days i have a slow 3g connection on my HTC one X+.
There is no slowness when i'm using wi-fi.

I tested 3g connection with speedtest app and i saw only upload speed is too slow (Download speed is around 12 Mbps and upload speed is 0.00 Mbps)
I called my gsm operator and they said it is not related with them.
Did you encounter such a problem?
Or do you have any ideas about it?

Thanks in advance.

Şaban