Keep trying. It will learn. My GF's name is not common - at all, and at first, siri had trouble recognizing it; after a few days, there is no trouble at all.
But tt Just dials Numbers I use regularly....? Maybe I should have started afresh? I don't get a chance to it...It just does it.
I had the same issue. So I asked who is my sister. Siri responded I do not know do you want to tell me. I told her and she asked do you want me to remember? I said yes and now she remembers. There is also a way to phonetically spell names in contacts which I think helps her get the harder to pronounce names.