DBA_TS_QUOTAS also contains information on the assigned quota, even if the user did not create any tables.
From the manual
MAX_BYTES
- User's quota in bytes, or -1 if no limit
Example:
SQL*Plus: Release 12.1.0.2.0 Production on Tue Oct 18 10:35:29 2016
Copyright (c) 1982, 2014, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
SQL> select tablespace_name, username, bytes, max_bytes
2 from dba_ts_quotas
3 where tablespace_name = 'USERS'
4 and username = 'FOOBAR';
no rows selected
SQL> create user foobar
2 identified by welcome
3 default tablespace users
4 quota 10M on users;
User created.
SQL> select tablespace_name, username, bytes, max_bytes
2 from dba_ts_quotas
3 where tablespace_name = 'USERS'
4 and username = 'FOOBAR';
TABLE USERNA BYTES MAX_BYTES
----- ------ ---------- ----------
USERS FOOBAR 0 10485760
1 row selected.
SQL>