Another thing MIGHT be, where are you from originally. Are you an EU citizen? They might be confused about that, and then timing issue then would make sense. Maybe your "work permit" in the US is not a permanent one in their eyes and if you are EU, then the long-term agreement stays regarding your retirement pension.

Here are two documents I've collected about Swiss Social Insurances with information about foreign nationals and leaving Switzerland. Perhaps you can pick through them and see what applies to you?

Sorry can't be of more help this morning!