Index name is not read from my logstash configuration [SOLVED]

[Axl (XYZ)]

I am a newbie to ELK, and this is very probably a n00b question.
I have set up ELK, and those are currently the indices that I have on my host:

curl 'http://localhost:9200/_cat/indices?v'
health status index                            uuid                   pri rep docs.count docs.deleted store.size pri.store.size
yellow open   filebeat-2020.03.10              9vYa2M9QR1-sBMtDnIaekw   1   1       1666            0    839.7kb        839.7kb
yellow open   logstash-2020.03.03-000001       035LbhSGRv-_yAW9UNV4Xw   1   1       2842            0      1.5mb          1.5mb
green  open   .kibana_task_manager_1           ca5hQQYIT62JKee4euSSHQ   1   0          2            2     20.8kb         20.8kb
green  open   .apm-agent-configuration         MAAyG6-zSWWl61C_0ne43w   1   0          0            0       283b           283b
green  open   ilm-history-1-000001             JcOJ8kX5TIWcPd1kSRCy3w   1   0         27            0     34.3kb         34.3kb
yellow open   filebeat-7.6.1-2020.03.10-000001 pvS64-dvSmekPbJNV8xZXQ   1   1     173561            0       45mb           45mb
green  open   .kibana_1                        oQN_ZPreTaifBdHEbq6paQ   1   0         25            8    227.7kb        227.7kb
yellow open   filebeat-2020.03.09              8hQ2yayeQuqanX8lRuVrKw   1   1      12363            0      7.1mb          7.1mb

I am using filebeat as you see, that sends data to logstash.
I do not understand where those indexes are configured . I thought is was in /etc/logstash/conf.d/logstash.conf, but it doesn't match... For example, my configuration states (see below) an index name of filebeat-DATE. But when I list my indexes, it turns out the index which is used is filebeat-7.6.1-2020.03.10-000001.

elasticsearch {
            hosts => ["localhost:9200"]
	     index => "%{[@metadata][beat]}-%{+YYYY.MM.dd}"
        }

• Can I safely delete the other filebeat indexes?
• How can I view the current content of a given index using CLI ? Is there a URL to grab for instance the last few records it got?
• Why isn't the name of my index filebeat-2020... as specified by /etc/logstash/conf.d/logstash.conf ?

Thanks for your help!
PS. I am using version 7.6.1 on Linux.

[Axl (XYZ)]

I got the reply from a user: this is because I use ILM by default. Therefore the name of the index is ruled by ILM, and not by what I specify in my logstash.conf file.