Hey! 😊
As someone already mentioned, Meera has 3 completed stories and she opened up her blogs currently. If you haven't, I would suggest you to give them a read, 2 of them are pretty long (3 volume stories) so they should tide you over for a long time 😆.
https://awordsworthbymeera.wordpress.com/
https://emeraldisletalesbymeera.wordpress.com/
https://ariverrunsthroughitbym.wordpress.com/
After that you can read Expelliarmus / Juhi's stories. They are on open blogs and IF as well. She has many completed stories and all in different genres. I'm sharing her index link from both blog and IF but her OS are not there on the blogs I think.
https://expelspells.wordpress.com/
https://arhitalesbyexpelandthemagpie.wordpress.com/
This last one is a go to link for short tales with many different genres and backdrops that will feel like complete stories but much shorter. Both of them are awesome writers and these are a quick read for when you're short on time but want some refreshment for the mind 😁.
Other than that there is PhattiSari whose work can be found on Tumblr, Fanfiction.net and Wattpad. She has an ongoing story too but there are many completed ones which you can find in her index on Tumblr.
https://phati-sari.tumblr.com/ipkknd-ff
Just sharing Jigs index, she too has a few completed works which have been reopened currently.
Lastly, I'll share this ongoing FF. I know you wanted completed one, but the reason for sharing this one is that there are nearly 50 chps up already and the author is pretty consistent with updates (1-2 updates per week). And the story + character development is awesome. It's called Birds of a Feather and the author is -Archi-
https://www.indiaforums.com/fanfiction/chapter/6257
When you have read all these, you can msg again on the thread or PM me. I'll share more stories that come to my mind 😳.
Happy Reading 🥳.
Love,
Stuti