Forceful Communication from a Software Company

I have received a call and an email from Corel Corporation India. Their claim is that my startup using 10 unlicensed versions and if I don't make them licensed then they can visit my premises to verify this. We don't use their software though we deal with the creative industry by using Adobe License. So I have replied very softly to their first email saying  "We do not have 10 PCs in our entire premises and we do not at all use Corel draw". I ask asked them to send the source of the claims so we can cross-check and revert. In return, they have sent me a "WITHOUT PREJUDICE" Notice via email. Here is a screenshot: Though it has some Grammar mistakes which could happen to anyone, what action should I take? Should I Send a legal notice? I also don't know the cost of the Legal Notice. :( I was thinking to reply them with an email saying  "We don't use Corel in our organization. Still, if you want to take this discussion further, then kindly share proof of illegal usage. You can visit our premises with a legal notice and all covid prescription ofcourse.We hereby put you into notice that if you fail to show the log proof or showed fake logs by mistake even or didn't proof of the claim after visiting premises, then we will take legal action against your organization. So share your company address, legal name, and authorized contact details." Please guide me.