as I know even cancellation of the flight by EU carrier doesn't mean right for cash refund - EU261 leave it to terms of specific carrier, Montreal convention allow carriers to reschedule without time limits. I was abandon by A3 in the middle of return flight, no re-seating to existed *A flights for 5-8 days. I even visited their so-called "representatives" in two airports only to find they are not authorised to care about passengers whos transportation A3 had started and not finished. Of course my contacts were entered into reservation and I am status passenger for A3 (only silver, but).
SO the result: even unused/cancelled part of that return ticket they are refusing to refund.