Have you made sure the WiFi is disabled.
You could also try restarting your router.
Why are you trying to reinstall Mac OS X El Capitan on your mac.
It is always better to have a means to reinstall the OS at hand and not rely
on Apples Recovery Servers.
I hope you have not erased your mac.
If you still have an operating system on your mac you can download a copy of El Capitan
then create a bootable USB flash drive installer and use that to erase your mac and reinstall.
Details below.
If you have already erased your mac you can do the procedure below on another mac, that mac
must be of an age where it could run El Capitan.
How to get old versions of macOS – Apple Support
Go to Download OS and click on OS X El Capitan 10.11
this downloads InstallMacOSX.dmg to your Downloads folder.
The next section can only be done on a mac that is capable of running El Capitan.
This includes macs that have the potential to run El Capitan but have been upgraded to a newer OS.
A mac that came preinstalled with an OS later than El Capitan will refuse to do the next bit.
When downloaded open to InstallMacOSX.pkg, double-click on
that and an installation window will open, this does not install El Capitan
but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which
you will find in your Applications folder, it should be 6.2GBs in size.
(If the installation window asks which disk you want to install to, you must pick
the disk that you are booted to at the time. Not any internal or external disk that
you want to eventually install El Capitan on, that is for later.)
Create a bootable USB installer disk using the Install OS X El Capitan.app in the Applications
folder and the createinstallmedia command in the Terminal app.
Read the instructions here,
How to create a bootable installer for macOS – Apple Support
