After a lot of communicating, I've finally been able to get a refund. If anyone else is having the same problem, I recommend contacting SPG customer service directly - not Starwood vacations. I spoke to a succession of agents at Starwood vacations who insisted they could not issue a refund and continued to offer me a ridiculously limited choice of travel dates that would be incompatible with any working person's schedule. After SPG customer service got involved I was issued a refund within a day. Thanks go to the people there for getting involved!