Doubt how to make a thread with select and cancel query executed in the database

I'm running a query within a thread and set a timeout for it to execute, or another way of stopping it would be for the user to cancel the select . The problem is that I stop the thread but the query continues to run in the database.

I had the idea to stop the query with a command of postgresql so I need the pid of the query, and then do the following select:

(
    SELECT
        p.pid
    FROM
        pg_stat_activity p
    WHERE
        state = 'active'
        AND query LIKE '%SELECT * FROM GCEPDC02, pg_sleep(%'
        AND query NOT LIKE '%FROM pg_stat_activity%')

But this select does not return anything, any suggestions?