Gentech LLC Apparent take over of PC by Gentech LLC Nationwide

Similar to a report from Rento WA, my pc was interrupted by an error message and a loud beeping when I tried to access an internet site.  The pop up note said there was a  Windows 10/internet problem that had to be fixed.  It stated a number to call and to not turn off the computer.  I called the number, thinking it was a Microsoft site.  I let them access my PC and they said my PC had mutlitple infections and needed their technician to take over my PC and fix the isssues.  The offer was to fix the PC virus issue and a 3 year coverage plan for $400.  I finally questioned the whole process - I didn't see how my pC could react so violently to my search and then ask to call 855-202-1840.  After a half hour discussion, I decided to decline the offer and to hang up.  Not sure if it is a scam or if Gentech LLC is reallly the company I was talking to...  My PC seems to be working ok.