score:1
Depends on your ticket conditions and the airline in question, but odds are pretty likely the answer is no.
What you have sounds like an open-jaw return: you've basically paid for A-B/B-A return as a single ticket, with a small surcharge to return from C instead. Airlines will generally not refund any portion of a return ticket after the journey has begun (= you have flown one half of it), and this applies to open-jaw returns as well.
A "true" multi-city itinerary consists of a series of one-way flight tickets tacked onto each other. These would usually let you refund individual segments, because they're separate tickets under the hood, but they also usually cost a lot more.
Upvote:1
Even if you cannot get a refund of the fare, you may be able to claim a refund of the taxes on the unused part of the ticket, which can amount to a significant proportion of its price. See e.g. here. The details depend on the country and airline.