Luciano,
When you look at the tablespace reports in CCR, there are two columns for SIZE of the tablespace.
If they are equal, then you can believe the % used column. If they are NOT equal then the % used is wrong. It will always sit near 90% used and then as needed more space is Allocated, until Allocated = Used size.
When rows are deleted from tables, the space is not shown as available unless you move the tables inside the tablespace. Then after the Table Move you will see free space. (Truncating staging tables is similar to a move and does show reduced table space.) Deleting rows individually from a table does not.
Here is more information on this subject: from Oracle click the link.
David