iPhone mail app not fetching mails automatically and have to every time go into the mail app and refresh it to see my received emails.

My iPhone mail app doesn’t fetches mails automatically. Every time I receive a mail, it never notifies me. Some times there is badge on the mail app showing unread emails, that badge too comes after half a day.

I have checked each and every setting. Even had my settings reset once when apple support told me to do so.

Due to this I was forced to use external mail apps such as outlook and gmail. But Apple’s Mail app is better and I would like if I would get to use that.

If anyone knows how to fix this, please let me know