Retrieving the account of a deceased family member

My Father recently passed away and I know for fact he had legal documents in his account which are crucial to help aid with sorting out his estate. We have tried contacting *** Email address is removed for privacy *** with no response. We called Microsoft support and they said this email address is no longer in use and directed us here to find another resolution to this. We have all the documentation necessary to prove our relation to my Father, that I am the next of Kin, and also proof that myself and my sister are the sole beneficiaries. It is important we hear back and have access to these accounts as soon as possible. Thanks