Why can't I get into my ipad?

I have had my ipad for a while now. I tried to use it 5 months ago and it won’t let me in. When I first got it my dad used his email to create the apple ID. Since then, he doesn’t use that email anymore and can’t remember the password. It has completely locked me out. I have spent many hours on the phone or over message with apple support and they haven’t done anything. I need my ipad for work. PLEASE HELP :(