I, too was Platinum for three days and now am back to Gold. With the 15 nights for being a new Visa Card holder and the number of stays I've had in the last year, I believe I should be Platinum. I wrote to Marriott and I'll wait for a response. On the bright side, I did get the Platinum amenity when I checked into a Marriott tonight.

The other odd thing is that I have 34 nights so far and it says I need 41 more to retain Gold.