Oracle db user quota not being revoked

I had a user, bob, who couldn't insert data into a table which resides in tablespace ts1. They got the lacks quota privilege error.

I granted the user bob unlimited privilege on the ts1 tablespace with:

> alter user bob quota unlimited on ts1;

I checked for the quota and it was there.

> select * from dba_ts_quotas;

The user bob was then able to insert data into table which resides in the ts1 tablespace.

At one point user bob didn't need that access anymore, so I did the following:

> alter user bob quota 0 on ts1;

I checked for the quota and it was no longer there, as expected: