The issue is that you have to prove that it was your account. If they did not require that people would be stealing each other's accounts by the thousands every day.
there should be an alternate email that they can send a link to or a phone that they can call or text or security questions that you answered once and have to answer the same way.
If you can't do any of that ( and how many options are available is dependent on how many you set up) than it is going to be difficult or impossible to get it back. Your best bet is probably to keep trying with different possible answers until you get the right ones.