Complex sentence: The format was changed to mainstream rock in 2001 when Corus Entertainment acquired the station, and the format was changed again to classic rock in 2003, but the Cool FM branding continued to be used and all those rock music formats failed to attract listeners.
Split into simpler sentences: The format was changed to mainstream rock in 2001 when Corus Entertainment acquired the station, and the format was changed again to classic rock in 2003. The Cool FM branding continued to be used and all those rock music formats failed to attract listeners.