On my Jenkins I configured:
Source Code Management
Git repository: https://bitbucket.org/username/project.git
credentials: username/
You don't need to enable Polling SCM..
You have to ensure that your Webhook (Settings->Webhooks) is pointing to your Jenkins bitbucket-hook like the following: "https://ci.yourorg.com/bitbucket-hook/".
Notice that last "/", without it, the build will not be triggered.
It's an annoying thing, as you will get a 200 status code from Jenkins when sending requests, with or without it.