you might want to try and call your local paper and see if they'll do something with you on this topic over christmas. overall people dont tend to look at adverts as it's like someone telling them what to do and people dont like authority, however a nice story about a kitten being given as a present and then unwanted after christmas will have a lot more affect on people.
also try your local bbc and commercial radio stations and see if they'll interview you.
this is what i'd do anyway, although i dont work or volunteer for an animal charity i do work in PR professionally and it is the nature that people don't react so well to advertising as they do to 'copy' - a story in the newspaper.
hope this helps!