Inherited bank stock

In 1977 my grandfather passed. In his will he left his grandchildren stock he purchased at a local bank. The will stated that the stock could be claimed when the youngest of us reached 18 years of age. My grandmother passed in 1978 and left us the same stock in her will as my grandfather had wished. We never knew about this stock he left us.

We were going through old papers and found a 1099 form from Citizens Central Bank dividends form dated 1978. This is the only proof we have other than the will that he left us stock in a bank.

I researched the history of Citizens Bank and it merged/was acquired by First American Bank, 1st American Bank was acquired by AmSouth Bank, and AmSouth was acquired by what is now Regions Financial Bank. I called Regions Investor relations and gave them my grandfather’s information and they could find nothing with his social and told me I needed a stock certificate number that we do not have. I asked for the transfer agent that handles stocks and they refused to give me that information.

I had my sister call and they told her she needed an electronic certificate, she told her that in 1978 they didn’t have electronic certificates and told her she was being rude by stating that. I called Regions investor relations 6 times after my 2st phone call and it is as of they have blocked my phone number from calling.

We have had this stock sitting in banks that have merged and changed names over 40+ years and they can’t find anything and are unwilling to assist us in locating the history of this stock and what happened to it. Things are looking extremely shady to me at this point. I feel like because it took us over 40 years to find it that no one ever expected us to claim it. Can anyone advise me of my options at this point?