Who has the right to claim a mutual fund without a beneficiary that is already withdraw by another person?

Was there a probate proceeding? Could someone have had a power of attorney the used while the person was still alive. (I'm assuming the owner has died with your question.) As for the place to call to learn about it, it depends whether the mutual funds were direct or held in a brokerage account. However, even if you can determine the appropriate person to call, you would have to provide them with sufficient proof that you have some legal rights / powers to discuss the account.

If the mutual fund did not have a designated beneficiary the it would be part of the decedent's estate at the time of death. A probate estate should be opened so the financial institution knows the identity of the proper heirs as determined by the probate court. It may be possible to use a small estate affidavit if the total value of the probate assets is less than $100,000. The court appointed representative would have authority to obtain documents relating to any decedent account for periods of time before and after the death of the decedent. If there is a Will then the Will determines who receives distributions from the estate. If there is no will (intestacy) then the statute on descent and distribution determines who receives distributions from the estate. With an intestate estate the spouse and children would receive distributions: spouse 50% and children 50% with the descendants of a predeceased child equally dividing the share of the predeceased child would have received if alive. If there is no spouse the children would share the probate assets.