Unless YOUR Apple-ID has a copy of that software on its "Purchases" page, it is not available to YOUR Apple_ID. It si no longer available as new, unless you have a Mac that cannot run the latest MacOS, Sierra.
The copy you were running before erasing was on your dad's Purchases page, so it is only available to him.
tjk posted the link to an article on what to do when you sell or give away your Mac. That should point you in the right direction. You may not need to do literally everything there, but it will give you the right idea.
Hi,
Ask your dad to do the following, and all should be well: https://support.apple.com/en-us/HT201065
Not sure why you need to install El Capitan, though you could be installing El Capitan with using your father's Apple ID.
OS X Utilities screen, new copy of OS X El Capitan not avalible
