the only thing to do with an ISP like that who sells more than their local throughput allows, is to COMPLAIN (or switch). If you do not have a better local ISP (dsl or cable), then your only option is to call and harass them.
In a "customer service" environment, the best way to get results is to complain and be as much of a nuisance as possible. Most companies will eventually get to your problem before others, just because you are consuming time with their customer service people and asking to speak with managers all the time, etc. Get on a first name basis with a manager or two, and you MIGHT have a chance of getting your area improved before they improve somewhere else. Provide your worst examples of bandwidth WAY below their advertised speed (the speed you are paying for!), and even try to demand discounts since you are only receiving part of your money's worth (it does not matter what time you want to use your internet, you are paying for a speed measurement they advertise).
It is NOT acceptable to have your internet speed regularly any significant margin below your advertised speed. In my opinion, you should constantly have within 500kbit of your advertised paid for download speed, or they are actually performing false advertising (in which case you may even have a court case against them!).