Boss: Did you get that X thing is done?
Me: Yes, that's done.
Boss: No that's not done, I am still getting calls from people asking for X?
Me: Oh, Perhaps/Maybe/I guess/I think you are asking about Y thing.
Here I was chatting with my boss, I doubt what should I use out of these if I want to make it more formal chat/email?
If none are correct, please suggest.