I have database Oracle 18c XE. After shutdown and startup is not possible to open PDF database. Error: ORA-12954: The request exceeds the maximum allowed database size of 12 GB

But size of datafile users01.dbf is 5,2 GB only. It is a bug?
What can I do with it? It is important to solve it quickly for operation of a medium-sized company.
Thanks for advice!
Jaromir