Did you recently port to zong or something?
I ported to Zong, and I was getting your speeds. Helpline couldn't really do much (they were going to launch a trouble ticket) until I told them I'm using their promo of 5,000 MBs, SMS and free minutes. The guy and I suggested perhaps it was because I wasn't signed up to a bundle package that I'm getting dismal speeds.
And lo and behold - when I subscribed to a bundle, my speeds rose quite a bit!
So - for those who aren't going above 512kbps on average, try subscribing to one of their packages (not their daily mini package - that didn't work for me either).
And also, not all speed test servers are equal - some work better than the others at different times and on different services, so you should try a multitude of servers before reading your result.