The Neighbor Is Driving Me Crazy

Photo is of area before we planted grass.
We added a room in the basement of our rented duplex, and installed an egress window in place of the normal basement window. When the workers installed the window, they left a layer of sand so now grass is not there. It’s on the side of the house, which is rarely looked at by us or the neighbors.
I received a call from the neighbor’s son, Mark, who does not live next door, that I better plant more grass. I spread seed and watered the area, so the grass would grow back. Mark called a week later telling me no grass had grown back and I’d better sweep up any sand on his father’s property. I went to Home Depot yesterday to buy sod, dirt, and seed to get the area growing faster. Mark called again, saying it was not good enough. I told him to mark his property with wooden stakes so we could put-up a plastic ground divider to separate our properties.
I’m doing my best to be kind and patient, but I’m near my wits end. What is his real concern? In sales, often the first concern is not the real concern. Any tips for dealing with difficult neighbors?
Deborah, editor of Little Love Tales