We also had these letters, mcycsnb, on our credit report showing it was open in 1981.
I looked it up in this blog and called MACY's. IT was a credit card now but in our case it was a old Famous Barr card. I guess the account even though it had a zero balance kept on going. Macy's apparently bought out a lot of stores over the years along with those credit cards.
We called Macy's at this number 1 866-593-2543 and spoke to a man who looked up my wifes name. It was a account she opened up before we were married. We had it closed, FINALLY!!!!!
Try that number, it might work for you. They can look things up without your SSnumber but they might ask for it.
Good Luck
Lennie