Can My Gcse Results Have Been Mixed Up With Someone Else’s?

I got my yesterday and found that I had got two Cs (one for my french listening and one for music). I don’t understand how this can be right as they are my best subjects and I’ve never even got below an A* in any mock in either subject. My overall grades were consquently lower than I had expected as well.
These two exams were both taken on the same day and at our 2nd school site (unlike all my other exams)
Is it possible my candidate number had up?
Please if you can help. I’m really disappointed and confused by these grades.