When Shabbos Chanukah falls on Rosh Chodesh, three Sifrei Torah are removed from the Aron. The first Torah is used for the parshas hashavua, the second is for Rosh Chodesh, and the third is used for the Chanukah reading. Since the final reading is about Chanukah, the Haftorah is also the Chanukah Haftorah. In addition, there is more pirsumei nisa if the Chanukah Haftorah is read. B’dieved, if the Rosh Chodesh Haftorah was read, it is not necessary to read another Haftorah.
[שו"ע תרפד, ג, משנ"ב יא, וביה"ל ד"ה ואם]