Did you give them a different credit card? If you do have them cancel that payment.
You should also contact AMEX and ask them to put your card on a watch list (if they have one). If you provided full information for the payment, they could resell that info to other hackers for them to use to make purchases. If you want to be extra paranoid or just for your peace of mind, have AMEX cancel and re-issue your card with a new number.
If you gave them "remote control" to your computer, then yes certainly they could have installed malware, or at the very least a "back door" that gives them access to your computer at any time they want. The same is true to a lesser extent if you went to their website.
Running the suggest antimalware is one way to get a bit of peace of mind. But the "gold standard" for wiping out potential malware problems is doing the already suggested "Clean install". You should use a DIFFERENT computer to setup the USB with the required installation files.
Here is some more reading about various Scam attacks:
2018 04 27- SCAMMED BY INFORMATICO EXPERTS? HERE'S WHAT TO DO - (LIVE PC EXPERTS) 1-800-701-2953
https://www.infopackets.com/news/10325/scammed-...
<snip>
I have been in contact with Informatico Experts Inc (Live PC Experts) since last November ... [and have paid them a grand total of almost $12,000 up until recently]. …
</snip>
2018 04 23- WINDOWS WARNING: TECH-SUPPORT SCAMMERS ARE RAMPING UP ATTACKS, SAYS MICROSOFT
https://www.zdnet.com/article/windows-warning-t...
<snip>
Windows 10 security won't protect you from tech-support scammers' lies and trickery.
Microsoft says it received 153,000 reports in 2017 from customers who'd come in contact with tech-support scammers via a cold call, spam, or the web.
</snip>
2017 10 17- HOW TO RECOGNIZE SCAM WEBSITES
https://www.lifewire.com/how-to-spot-a-scam-web...
PHONE SCAM
For the most relevant information on Microsoft Tech Support Scams, please visit the Microsoft Tech Support Scams page (
https://www.microsoft.com/en-us/wdsi/threats/su... ). We (that is “real” MS Speaking) can ensure this page stays updated with the most relevant information involving support scam trends, techniques, and solutions.
ADDITIONAL WAYS TO IDENTIFY SCAMS
https://www.groovypost.com/news/beware-of-windo... Windows 10 Activation Tech Support Scams
https://www.microsoft.com/en-us/wdsi/threats/su... Tech support scams
https://www.microsoft.com/en-us/safety/online-p... How to recognize phishing email messages, links, or phone calls
https://www.microsoft.com/en-us/safety/online-p...
FUN WAYS TO SCR*W WITH ‘TECH SUPPORT’ SCAMMERS
http://techgenix.com/screw-tech-support-scammers/
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SERIOUSLY, SOME “RESPONSIBLE” THINGS YOU CAN DO ABOUT SCAMERS
HOW TO: REPORT THE MICROSOFT PHONE SCAM
https://www.microsoft.com/en-ca/reportascam/?lo... – Report directly to MS
https://cloudblogs.microsoft.com/microsoftsecur... Contacts to Officals in USA, Canada and UK
https://www.ic3.gov/complaint/default.aspx US FBI Internet Crime Complaint Center (IC3)
REPORT A TECHNICAL SUPPORT SCAM TO MS
https://www.microsoft.com/en-us/reportascam/
Microsoft takes seriously its commitments to protect and maintain the privacy of its customer data and empowers its customers to implement and use our services in a protected manner. Unfortunately, technical support scams have become all too common across the industry, affecting consumers worldwide. Customers, family, friends and Microsoft employees are receiving unsolicited phones calls and pop-up advertisement from fraudsters claiming to be from a reputable company or a partner of Microsoft.
MS PIRACTY / BOOTLEG INFO SITE
https://www.microsoft.com/en-us/piracy/default....
WAYS TO BLOCK UNWANTED CALLERS (US)
https://www.consumer.ftc.gov/topics/limiting-un...
https://www.donotcall.gov/
2014 0 17 APP STORE- THE WINDOWS STORE IS A CESSPOOL OF SCAMS — WHY DOESN’T MICROSOFT CARE?
http://www.howtogeek.com/194993/the-windows-sto...
Microsoft’s Windows Store is a mess. It’s full of apps that exist only to scam people and take their money. Why doesn’t Microsoft care that their flagship app store is such a cesspool?
AVOID SCAMS THAT USE THE MICROSOFT NAME FRAUDULENTLY
https://www.microsoft.com/en-us/safety/online-p...
2016 09 14- BEWARE OF MICROSOFT SALES REPRESENTATIVES POSING AS AUDITORS TO SELL OFFICE 365 – LICENSE – SCAM - REVIEW
http://www.techrepublic.com/article/beware-of-m...
<snip>
User reports indicate Microsoft is using the spectre of fines for noncompliance to upsell businesses on Office 365, the SaaS version of Microsoft Office. Here’s what to look for and how to respond.
...
.
For a bit of inspiration, the OSS Simple Sabotage Field Manual offers surprisingly relevant tips for frustrating sales representatives to the point that they may give up on pursuing your organization.
.
See also
• Report: Unused enterprise software is costing businesses a fortune (TechRepublic)
• Microsoft offers free Windows Server 2016 licenses to VMware switchers (ZDNet)
• Windows 10: Microsoft forces you to choose between privacy and security, say campaigners (TechRepublic)
• How to remove unwanted apps from Windows 10 (even though Microsoft doesn’t want you to) (TechRepublic)
• 10 books to get you started on big data: TechRe
</snip>
SCAM PHONE CALLS
http://techgenix.com/screw-tech-support-scammers/
The author of this article lists several “games” you can play when you figure out you ae getting one of these scam calls.
THE “TECH SUPPORT” SCAMMERS CALLED HTG (SO WE HAD FUN WITH THEM)
http://www.howtogeek.com/180514/the-%E2%80%9Cte...
The author documents the process followed in one of these scam calls