Private Name, Private Number

I refer to my grandchildren as Angel and Armoni, their birth names. However, a message left by my grandchildren' adoptive mother on our answering machine, caller id reads private name private number, referred to my grandchildren as other names. My question is, how is this in the best interest of a child. Reminds me of slave owners changing the names of their slaves to erase all traces of who they are and to which family they were born into.