Unable to delete auto-generated rhel-client from sensu core 1.9

hi,
we are using sensu core 1.9. even we did not added client name rhel-client in our environment is continuously displaying on sensu dashboard and also continuously triggering the email alerts. for keepalive and postgres checks.

tried to remove but still appearing
curl -s -i -X DELETE http://127.0.0.1:4567/clients/rhel-client

please provide solution