my cable drops down to nearly nothing when the neighbors are downloading movies or what not. this can go on for 5-8hrs at a time

by nothing I mean 700kb/s down or less. one time there must have been 3-4 people downloading and it slowed to a crawl 10kb/s took forever for the dslreports speed test to finish. it was around 9pm so i just said screw it and went to sleep