Postgresql – unable to drop database because of some auto connections to DB

Whenever I try to drop database I get:

ERROR:  database "pilot" is being accessed by other users
DETAIL:  There is 1 other session using the database.

When I use:

SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname="TARGET_DB";

I terminated the connection from that DB, but if I try to drop database after that somehow someone automatically connects to that database and gives this error. What could be doing that?
No one uses this database, except me.