There is an app these people use to make the phone number appear as if they are from Interval International. They asked me for money and as I had already  paid for the 5 year Gold Membership, they said that was just for the upgrade from a blue membership and I still owed for the Basic Blue Membership. Having received a number of these calls concerning other scams, I requested a letter from Interval International stating what the caller had said and that I would  then phone them. They said this was expensive and they don't work that way so I told them where to go and followed it with a loud Good-bye.