The Ophiuchi hotline - John Varley

Following the effortless capture of Earth by vastly superior aliens, humanity was left to fight for existence on the Moon and other lumps of airless rock. Survival was greatly facilitated by the interception of the Hotline, a constant stream of data from the direction of a star in the constellation Ophiuchus, which enabled the development of amazing new technologies. Four hundred years on, and everything is about to change again because humanity's unknown helpers have just sent what appears to be a bill.

It shouldn't matter to Lilo, since she's been caught experimenting with human DNA and sentenced to permanent death for crimes against humanity. But she is rescued by the maverick ex-president of Luna and finds herself - and several illegal clones of herself - caught up in a crazy attempt to liberate Earth from the vast inscrutable entities who have conquered it, and in the sudden emergency that the enigmatic bill presents to all of human civilization...