This "new" SA has been very helpful, but are you also unhappy with your original SA? Like SoCal, I also thought this one helped you find the birkin? If you are still happy with the original SA, I would do what Nom de Plume said and tactfully arrange to work with your original SA.
It actually seems like an issue between the SAs--When I called yesterday and asked for my SA, she was at lunch--the one who answered the phone offered to transfer me to my SA's voice mail, checked quickly for a scarf for me, then took a message for my SA. She did not volunteer to help me herself--I wonder if they have an official policy on this? Are they supposed to offer to help you, so the customer is always happy, or are they supposed to make you leave a message for "your" SA to avoid stepping on each other's toes?