Refund Steps:
Visit https://us.battle.net/support/en/help
Click “Diablo 3”
Click “I would rather categorize the issue.”
Click “Payments”
Click “Refunds”
Select the reason for refund
I believe, however, there’s usually restrictions on being granted one, i.e. you must request it within a short time period from the date of purchase, and you must not have played it, or played it very little.
That brings us to your Necromancer Anything which was “Last updated on 12 Nov 2019 18:58 GMT” which means you’ve had the Necromancer DLC for at least 20 months.
If we look at your Career Page it shows that Necromancer accounts for 13% of your entire play-time, second only to Witch Doctor, but ahead of the other five classes.
Your Career page also shows “Last updated on 30 Jun 2020 13:42 BST” which means you haven’t even played the game in over a year.
Short version
You won’t get a refund.