Hello Rob_Canada,
Thank you for using Apple Support Communities!
We understand from your post that you lost your contacts after updating to iOS 14.3. Are you sharing your Apple ID with another family member? That would be the reason their contacts are showing up in your iCloud account. If they saw your contacts on their device they could have deleted them which would have deleted them from iCloud and removed them from your device.
If you are sharing an Apple ID, one of you should create a new Apple ID and sign out of the shared Apple ID. Then sign back in with the new Apple ID so you are no longer sharing an Apple ID. This article will provide you with steps on how to create a new Apple ID:
How to create a new Apple ID - Apple Support
Once you have your own Apple ID, use the steps in this article to remove the old Apple ID and sign in with the new Apple ID:
What to do after you change your Apple ID or password - Apple Support
Once you each have your own Apple ID you can set up Family Sharing so you can continue to share apps and purchases if you like.
Set up Family Sharing - Apple Support
Best Regards.