LG
Please don't flame me, I say this with the best of intentions - like CrazyMadMan, I also have no problems on Brixton 126 when I connect during the day at work, and I am closer to the tower than you, although I connect from a fairly high location (so the overshooting signal might not apply to me).
Sorry if this has been asked or stated before. But, out of curiosity, are you using any directional antenna? Have you tried connecting from a different location to establish as to whether your problem might be related to your location? If the problem is related to your modem or account, have you tried a different modem?
Since I work close to you, I am willing to let you try my modem during my lunch time, no charge. (Email me through MyAdsl). No, I do not work for Sentech.