Notice Of Subpoena

I reported a client for something criminal when I was a social worker years ago. I got an email from a prosecutor saying that I should be receiving a subpoena concerning that case soon. I have questions.

If I call the prosecutor to ask questions, do I legally have to answer his questions?

They might not have my current address. Is it inadvisable to speak with the prosecutor about the case if I might not receive the subpoena?

I know this client evades court cases and I now live very far away from where the case occurred. Am I going to have to fly there every time they try to get the client to appear, or something?

The case involves footage of the client abusing someone. The prosecutor said that they can't use the footage that I gave to the police without me. I have never owned the footage, which was recorded by the company I worked for in the building I worked in. I have no access to it. I am also not in the footage-- why would they need me for this?

Is there a way to quash this subpoena?

My intention when reporting the case was to protect a vulnerable party, not to get this client in trouble, and punishing them for the crime would very likely not help them at all... obviously a consequence of reporting them, but I wish they'd get rid of the case.