are you using a router? or direct connection? you need to check to see if anyone is hijacking your wifi, and check speeds when directly connected to the modem. it doesn't look like you're being managed, cause you would get 25% of bandwidth ie 2.5meg.
also please post you're modem levels, see here
for how, and someone will let you know if they are cool
also have you checked the service status page for problems? its here