What can I do if my mobile unintentionally transfers contacts?

I have a huawei p20 pro and recently my dad got a huawei too and after a few months it suddenly transferred my contacts on his phone without us doing anything and without us doing anything and without linking the cell phones So what am I doing now?

Do you have the same Google Account?

Then you would have to turn off the sync. The strongest on both devices.

Since you probably uses the same Google Account.

And then that's normal.