Just called to the number on the back of my Platinum to cancel it. After entering it through the automated system, I was told their department was closed at this time.
Logged in to the web site and used the chat function. Was told there was a retention offer, but I would have to call to find what it would be. I proceeded with the closure of my account. Just can't justify $550 when the only thing I really use is the Hilton Gold and SPG Gold. Everything else is basically duplicate with my Chase Sapphire Reserve. From what I read in this forum so far, I don't think any of the retention offers previously reported would have been of interest to me.