Cancellation fee charged for their mistake

We booked a sever night MSC-cruise through CruiseAbout, on 26/05 through Rencia Kotze. We booked a cruise from Durban- Portugese Island-Madagascar-Durban. On Sunday, I saw an ad in the Rapport about all the MSC-cruises on offer. Our spesific cruise was not on that list, but showed that the cruise will not go to Madagascar, but to Ille de Mozambique. When I phone the travel agent on Monday morning, 1 June 2015, she confirmed this. She told me that the Simphonia can not go to Madagascar because of it's size.. I told her, that we are very dissapointed in that, as that is the reason why we booked. She told me that we can change our cruise to another cruise or get a refund. My husband and I decided to cancel as there was no alternative 7- night cruise (with different itinerary) that we were interested in. It was at this stage that the travel agent told me (02/06) that in that case we can get a partial discount and not a full discount, as the MSC takes a R3000 cancellation fee. I was highly upset, the reason for our cancellation was not because of our neglegence, but due to the fact that they changed their itinerary. They sold us something that they can not provide, and now I must pay.