linux – Unable to delete file in Centos

I can’t remove certain file in Linux. Here the example:

[root@HBL01 home]# ls -ltira index.php 
393591 -r--r--r-- 1 apache apache 14335 Nov 23  2021 index.php

[root@HBL01 home]# rm -rf index.php 

The file exists:

[root@HBL01 home]# ls -ltira index.php 
393591 -r--r--r-- 1 apache apache 14335 Nov 24  2021 index.php

[root@HBL01 home]# lsattr index.php
--------------e----- index.php

I try to write something with vim but appears at the end this message:

"index.php" [readonly] 17L, 14335C

Tried to change the permisos but… not run correctly:

[root@HBL01 ]# chmod 777 index.php 

[root@HBL01 ]# ls -ltra index.php 
-r--r--r-- 1 apache apache 8230 Nov 23  2021 index.php

What exactly happend? How can I remove this file?

Thanks in advance!