How exactly did you do this? It didn't work for me
Sent from my SAMSUNG-SGH-I317 using xda premium
I installed Dropbox from the playstore because I wanted to test the cloud feature.
I signed Into Dropbox in the app I downloaded (from playstore and in the settings under cloud)
I removed the dropbox app because I realized I may not need it with the cloud settings
When I was uninstalling (using regular methods [app info]) A message popped up saying dropbox would revert to factory settings and I hit ok.
I got an e-mail from dropbox saying I got an extra 48gb of storage for 24 months
Those were the steps I took. It kind of happened on accident. Didn't know beforehand that it would do that but it worked somehow.