While people sometimes suggest ignoring it because they say that your ISP is only sending you those notices because the laws compel them to and you downloaded something that was tracked, you may want to evaluate your risk.
Nothing has happened so far. Could something happen in the future?
Your ISP has built an entire portfolio of the things you’ve done online and which content you pirated. Who know how long your ISP retains that data, or which companies or regulatory bodies it shares this data with?
Laws may change.
Up to you on what you want to do with this information.