Dismal internet speeds

I recently decided to upgrade my adsl line speed from 2mb/s to 10mb/s. My prior line speed at all times averaged at about 1.5 to 1.9 mb/s. I now pay quiet a bit more for a faster line but I am experiencing speeds below what I had with my 2mb/s line. It peeks to 3.4mb/s for exactly 132ms then it bottoms out at 0.9 to 1.5 mb/s. Why must I pay more for a slower line. After what I have experienced from my adsl for the past year I could not be happier with Telkom, great service great attitude and value for money. So imagine my disgust and sour taste left in my mouth after supposedly upgrading and ending up with slower speeds.