OK, after a little research I came up with the following:
Prudential is still in business and the phone number is 1-800-778-2255. If they can't help you at that number, try 973-802-6000, this will take you to their corporate office and they should be able to direct you from there.
Northwestern National Life was acquired by ING in 2000. I would try 1-877-250-7171 and see if they can help you. If that number doesn't work try 1-612-342-7537.
Have the insurance policy number handy. They may ask you a few questions to ID the policy holder.(social, date of birth, etc.)
Hope this helps. Let me know hows this turns out.
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