Yes, it is illegal in America to have a Monopoly, we can thank Ol' Teddy Roosevelt for that one IIRC.
The government is allowed to maintain state-owned monopolies though, like the water and electricity companies are govenment owned and no one is allowed to compete against them.
However, some companies use tricks with copyright laws to pretend that they have monopolies on things.
How do you blame that on the Charter company?