My contacts keeps on duplicating on icloud?

If it keep happens it means you have a Mac with a corrupted contacts accounts that overwrite your "resolve duplicates" action

I had this issue for years, a month ago solved and still never happened again.

I don't know if this is your scenario but it was for me:

• have at least two apple device: a Mac (mandatory) and any of iPad or iPhone
• You sometime find duplicates in the contacts app on both Mac and the mobiles device/s
• If you solve duplicates they appear back later, not always the same ones but in random way

And here's as I solved, be sure to have a backup.

1. Use iCloud.com as the only source of truth, login and check your contacts are ok only on iCloud.com, mobile devices and Mac cannot be trusted if you have duplicates you can resolve them on any mobile device you have, when you're ok with your contacts list on iCloud.com proceed to step 2
2. Disable the iCloud contacts feature on all your devices (Mac and mobiles)
3. Only on the Mac completely erase the contacts folder from ~/Library and Caches folders, there are several tutorial available online.
4. Reboot all of your devices and enable back the iCloud contacts features, in some minutes you should see contacts appear in the app, on MacOS it could take longer than the mobile devices.

From now on you should no more have duplicates appears

Good luck!

one more things, when you disable the iCloud contacts the OS will ask if you want to preserve a copy of the contacts on device, answer NO, wipe the locally stored contacts as they will be recovered by the iCloud account later.

notable things:

1) Be absolutely sure your contact list is OK. on iCloud.com before wiping infos on the devices

2) Backup any folder on the MAC before deletion

3) Have lot of patience with MacOS, I don't know why but sync from iCloud on Mac is slower than on mobiles so don't panic if you see few contacts at first they will continue to add few at time, it took 10-15 minutes to have the contacts app on MacOS with all my 575 contacts

Ciao!

See this article.

If you see duplicate contacts after setting up iCloud Contacts - Apple Support