Let’s Encrypt won’t revoke the certificate, take a look to this post from ISRG Executive Director.
What you should do is report the scam site to Google Safe Browsing and Microsoft SmartScreen (I don’t use Internet Explorer but I think you can report a phising site from IE directly).
Edit: Here a site that explains how to report a malicious site from Internet Explorer. I’ve already reported it to Google and Microsoft.
Edit 2: Changed the link to Google Safe Browsing, I used the link to report malware instead of the link to report phising.
Edit 3: I’ve checked again (2017-May-03 at 07:20 UTC) the scam site and it is flagged as scam already (at least using Firefox browser).