You should not ignore this. However if you have not actually downloaded anything, then you have not committed any kind of infringement and the client is entitled to nothing.
You need to tell them that.
You need to tell them that you have no knowledge what they’re talking about and ask them to tell you what it is that you are alleged to download and on what date and then, you will get back to them. Tell them that unless they refuse to tell you that, you cannot provide them with any further information and that if they proceed to court without giving you that information you will raise this correspondence as evidence of their clients unreasonable and premature behaviour and you will ask the court to award costs against their client.
Ultimately, if you haven’t downloaded anything, they cannot produce any evidence. They are probably on a fishing exercise.
Don’t try to deal with this on the telephone, you will be wasting your time. All your responses need to be in writing.
Thank you for letting me assist you with your legal question. I am glad that I was able to help.
I am not certain whether that answers the question for you or not, but I am happy to answer any specific points arising from this.
It will be my pleasure to help you again either further with this or any future questions you have