I have found the best way to deal with this is the following

If you can have the cable company turn off the user name and password set to the cable modem if you can't log in to the modem itself.

Use the router to then use input the correct login info. I do this becuase most routers I have dealt with will allow you to check to see if it is still online at a set interval (mine is 30seconds, linksys wrt54g) and if it is not it will reauthenticate. This has solved 99.9% of my reset problems.