I get 2 or 3 calls from this number every day. I don't usually answer called from unknown callers & no messages are left. I answered once; no one spoke to me but I could hear people arguing about whose turn it was to take out the trash.
Yes it is United Healthcare. (Badgercare) They are contacting you in regards to your pollicy or to answer any questions you may have concerning you or your childs healthcare needs.
Make sure you're viewing the number correctly before misleading people who are receiving calls from 414.326.4321.
HIPPA laws may prevent the caller from disclosing who they are unless they reach the party they are trying to get in contact with, or how they are able to leave messages on voicemails, inboxes etc...
If anything, block your phone number and return the call. You will find out it IS United Healthcare.