Sure,
I think you are entitled to (at least) a refund for the 'unused' part of the flight based on:
Regulation (EC) No 261/2004 of the European Parliament and of the Council of 11 February 2004 establishing common rules on compensation and assistance to passengers in the event of denied boarding and of cancellation or long delay of flights
See under (5) and in particular Articles 4, 7 and 8.
EUR-Lex - 32004R0261 - EN