Deceased Grandma bought me Disney stock 20 years ago, how do I access it?

So in some time between 1999 and 2002, my grandmother bought me an undisclosed amount of Disney stock. I do not have any account information, but I did check www.missingmoney.com to find that I have four dividend payments in my name that went unclaimed in Ohio. I am listed as owner, and my deceased grandmother is listed as “co-owner.” I have visited https://shareholder.broadridge.com/disneyinvestor/ to try an access my stocks, but I do not have any of the account information. When calling the aforementioned agent, I am met with requests for account information that I do not have.

I want to see how much those stocks are worth, and then cash them out. How would I go about doing so?

Thanks.

EDIT: After speaking with an agent on broadridge, I was given a phone number to call. They input my name and confirmed with SSN and are sending my unclaimed dividend checks to my house with documents that will include with account number. Thanks everyone for your help/guidance.