Tom, this phone call is about your SSI benefits (Supplemental Security Income) . This program is only administered by the Social Security Administration but it does NOT come out of the Social Security Trust Fund.
Because there is an income and resource limit connected to SSI; they are calling you about this because they do monitor these income and resource limits closely.
Because the local SS offices are closed to most business and many of the staff are working remotely, phone interviews for SSI are now a normal course of business and they do send a letter beforehand so that you can be prepared to answer whatever their question(s).
I cannot answer your specifics but I do know that many SSI recipients had a problem with the over the limit ($ 2000) income reporting connected to Covid stimulus funs. These funds were not supposed to be counted - at least not for awhile. Most likely they need clarification - they already have your specific personal info so they will know what they are asking about specifically, and you won't need to supply any personal info like identifying numbers for yourself or your bank.
I hope they called on time but if not they will ASAP - I have heard that sometimes these times are just ballpark - as long as they have the right contact number for you. If you need to ask more questions, there are some knowledgeable people, some who work for SSA and are very familiar with the SSI (Supplemental Security Income) program, at this site and you can ask question there; just identify your benefit as SSI because there is a world of difference in SSI and Social Security of whatever type - Reddit.com Social Security and SSI Board
It's Always Something . . . . Roseanna Roseannadanna