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

I try to remove the file (no output) but the fie persists.

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

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

[root@HBL01]# ls -ltrh index.php
-r--r--r-- 1 apache apache 8.1K Dec 11  2021 index.php

[root@HBL01]# fuser index.php

[root@HBL01]# ls -ld index.php
-r--r--r-- 1 apache apache 8211 Dec 11  2021 index.php

What exactly happend? How can I remove this file?

Thanks in advance!

Problem persists:

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

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

[root@HBL01]# ls -ltrh index.php
-r--r--r-- 1 apache apache 8.1K Dec 11  2021 index.php

try this:

chattr -i index.php; rm -rf index.php

Is the file writable, it doesn't appear so? chmod +w index.php and then rm -rf index.php OR in one (pastable) step;

chmod +w index.php; rm -rf index.php

If no result, try creating a file in this same directory, and then performing an ls -al, and then consequently deleting the newly created file. This can be achieved as follows:

touch filename01.tmp; ls -al filename01.tmp; rm filename01.tmp

Give it a shot and let me know how it goes. If no go, please paste any output the 2nd command provides. It should give a listing of the filename01.tmp file you create. We can possibly learn something by doing this that will lead to an solution.