I can only guess … many Samsung owners have had a frustrating time at this stage (#metoo !). If you are getting the timing / switching right … then I expect that the flashing of recovery went wrong.
Is your phone on regular Samsung stock ROM – another Custom ROM might interfere, all /e/ instructions should be from a starting point of manufacturer’s stock ROM meeting this advice
Caution: Do not install /e/OS on top of a higher version of stock OS. Before installing /e/OS ensure your device has the latest stock OS of the same version as /e/OS. If only lower versions of the stock are available then install the last available lower version before installing /e/OS.
Did you try a different /e/ Recovery ? You could try https://eu.dl.twrp.me/starlte/ if you thought the /e/ Recovery was at fault. With TWRP one would usually try the latest version first, but you might try the latest TWRP 3.6 in this case.
Have you had the phone in use with wifi + SIM card previously … have you studied the Download mode screen with a magnifying glass for clues (post an image here, if you like) … are you facing one of the issues in the #Bootloader locked section of the Know your hardware - Samsung page ?