That happened to me on Days 3 to 6 of my switch from Orange LLU to WBC in April 2011. See http://forums.thinkbroadband.com/freeserve/t/3997115...
et al for how I fared and what I did about it.
At that time it was only giving me 11 Meg Down @ 15 dB NM and only 444K Up. I am now getting 20 Meg Down @ 3 dB NM and 1.2 Meg Up. But I had to write formally to them to achieve this.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC