Can I do an EPQ on something covered in class?

I have been working on my EPQ focused on child development/parenting. I asked both of my psychology teachers if I can do this EPQ and if there was a lot of overlap, both said it is fine to do. Now, they both told me I can’t do it?? I’m so frustrated as I made sure to get permission beforehand but now I’m being told it wasn’t true… the only overlap is one bullet point about infant/parent interactions whilst I’m doing parenting methods… but in an EPQ you go into so much more detail than one bullet point in a specification anyway? Can I do any overlap at all? A teacher even told me I can’t do an EPQ on child psychology AT ALL…