Posted 06 April 2009 - 07:56 AM
Any time you have have your browser open, or an internet connexion established, there is background packet "noise" of handshaking. While this is minimal, it can make a difference over a month. There are all sorts of free usage monitoring applications available for download; using one will enable you to better understand (both at the time as well as a cumulative monthly total) precisely where your limited amount is being "spent."
"Shouldn't they slow it ONLY when I've reached 12000 MB and not before?"
I would discuss this with your providor's representative after reviewing agreement information (either provided to you at the time or on-line).
Whereof one cannot speak, thereof one should be silent.