NOT A LAWYER
You really need a lawyer rather than a teacher, though it may be that some teachers have had experience of this.
If, as you say, you have not copied directly from any book, then you should have nothing to fear. I suspect that the onus will be on them to prove that you have infringed copyright (but check with a lawyer if this organisation threatens legal action).
Ask them for details of which books/sites you are supposed to have copied from. Certainly do not pay a penny before you receive this information. After you have received the information, check carefully to make sure that you did not, inadvertently, use somebody else's material. If you didn't, then consult your lawyer. Actually, if you did, consult a lawyer!
Don't be nervous if your notes are similar to those of others. It is very difficult, if you are writing notes or exercise for learners, not to say what several people have already said. If, for example, you have said that the present progressive/continuous is often used for activities going on at the moment of speaking and for arranged activities in the near future, you may well have used exactly the same words as half a dozen writers. That does not mean that you have stolen their words any more than it does if you use the sentence, "If you heat ice, it melts" as an example of a zero conditional.
- For Teachers