HDFC Bank Securities — demat account transfer

My father passed away 5 years back. He had a demat account jointly with my mother. However my mother name was registered as her marital name. However all her documents have her maiden name. We have been trying to find a solution for this for the last 4 years but we have been unsuccessful. Need an explanation for the same

We have been following up through the bank where the demat account has been opened. Every time a new problem is told and the application for transfer of shares are getting rejected. The bank officials do not have a clue on why and how the problem needs to be resolved and is always talks of the corporate office.