By DMAT a/c you probably mean a/c that pertains to equity shares.
The Bank may believe the following and may agree to pay to Nominee.
If a/c holder and/or all joint holders and/or last surviving joint holder: are deceased then nominee shall become entitled to interest in the shares.
Upon the death of a/c holder and/or all joint holders and/or last surviving joint holder: as per the applicable laws of succession in India, a beneficiary under the will of the last surviving joint holder, if any, will be entitled to the interest in the shares.
Both of above for DMAT a/c , FDR, seem to favor you, since you are both nominee and beneficiary in the WILL.
However you may not flaunt the WILL and obtain proceeds based on valid Nomination.
As in case of WILL the bank may have its procedure e.g; NOC from all legal heir and/or probate from court of pecuniary jurisdiction.