I’ll assume you’re using Win Server 2012 with that version of WSUS. Might want to start over here because if things aren’t done perfectly with WSUS integration, things get messy. You may have ran the WSUS installation past the point of configuration, meaning you don’t actually configure WSUS at all after you install it because SCCM will do all that for you. Try the following:

1.) Uninstall SUP role

2.) Uninstall WSUS

4.) Delete SUSDB from SQL Server

5.) Restart Server

6.) Install WSUS (make sure to not configure anything except for the ports

7.) Configured Updates to be stored locally

8.) Install SUP role in SCCM and configure the remaining settings. (Choose your updates, etc)

Finally, run a synchronization and you should see items start downloading. Check your wsyncmgr.log, wsusctrl.log and wcm.log to help diagnose any further issue.