I just got a rejection from a market from which I have no active submissions. Sadly it's not one of those lovely organized ones that gives you a submission tracking number or replies directly to an e-mail, so I can't see what was rejected. They just will not be able to use "your story." (It's a fairly limited market, so I'm absolutely sure I have no active submissions there.)
This is one of the times where it's really good to be experienced in the business, because I can shrug and go, "Either staff turnover or computer glitch," and joke about really REALLY not wanting whatever I sent them last (I believe I had a hat?) and move on with my life rather than panicking about what I did wroooooong to get rejected twice, so emphatically, maybe they want me to never submit there again even though they've published me before, or, OMG, maybe I accidentally submitted something that was totally wrong for them and now they hate me OMG, and...seriously, folks. This is one of the reasons being 80+ story sales into your career is so much better. Not everything is tinged with frightful significance. Editors are human, publishers are human, and they have moments of confusion and computer malfunction, and everybody goes on without the obligatory panic and overthinking.
I post this even though the people who are still in the panic and overthinking stage will probably have to get through that stage themselves, with their own experience rather than mine, just to say: hey. You, too, can come out the other side and mutter, "Mornin', Ralph. Rough day, huh?" at the editors. It will be okay.