Basis on inherited metlife trust interest shares.

 I inherited my fathers Metlife Trust Interest shares that were allocated to eligible policyholders as a result of the demutualization and are held in the MetLife Policyholder Trust (the “Trust”) in book entry form. These shares are held electronically with Computershare as custodian of the Trust.  I have sold all of the shares and was told by Computershare that that my basis is "0".  I believe that since I inherited the shares that my cost basis should be an average of the lowest and highest price it traded at on the day of his death.  Am I correct?

Thanks for any help the community might lend!