Screwed things up trying to setup WhatsApp--HELP!

Got my first iphone12. (I'm an author and use PC.) Asked my husband to delete EVERYTHING I'd not use. Friends who live abroad asked me to install WhatsApp so we could talk. I went to iphone Settings to install WA. I needed an (iphone) Apple account, which I did not have. I started setting it up. It asked for my email. I entered it but it wasn't accepted--the email was already taken or some such thing... (?) ATT is my email server. So, I thought, I'll create a new email with my pen name. Here's the problem: instead of going to ATT and creating the email FIRST (making sure it would be available!), I entered the one I planned to create... Big mistake: someone else already had that exact address... So, when I had to verify my email address for Apple, I was unable because the code they sent was sent to someone else. I created an online (website) Apple account, hoping it would somehow work (by now you realize how technologically illiterate I am). It didn't. I called Apple 800# and explained (or tried) the problem. The lady could not understand and after 20 minutes I thanked her and gave up. I'd be grateful for suggestions on how to fix this. Thanks.