Fraud from Webroot or Pretender

Last week I called Webroot about unwanted popups on my P.C. I was connected to "Steve Thomas" with an Indian accent. He gained access to my computer via "helpmeet.net" and trolled around in my Dell for 10 minutes or more, and then send me a report that my Dell had 500 viruses or malware that were slowly eating or destroying my Dell P. C. He said he would connect me to a P.C. specialist who would fix evryting remotely for a price of $199.00

At this point I became suspicious. I had been lulled since at work tech support often helps the user by taking over the computer via Baumgard, so I was not suspicious until he wanted $$$.
He gave me the call back number: 1-844-400-9538. John Cooper and Steve Thomas

When I returned home that evening I learned that there was fraud on my Amazon account and my credit card account. I cancelled both.

How could it happen that I called Webroot for help and got hijacked and defrauded?