BrianT,
While the above may help in adding MORE tablespace for data, this doesn't reduce your current usage, but is definitely a good option to increase your space as needed.
It sounds to me like you may be running out of actual space on the system. Either way, there are automated processes that will go through and purge the empty tablespace from incidents that have been deleted on a nightly basis. This is usually set to run late evening, early AM. There is also a way to do this manually if needed, but we would suggest talking to an Oracle DBA to do this, or work with support to ensure the process is being done correctly without impacting the other incident data.