Hi Philip. I'm Greg, an installation specialist and 9 year Windows MVP here to help you.
You'd need to contact the 3rd party antivirus you're paying to protect your PC.
I would uninstall any 3rd party antivirus in Settings > Apps > Apps & Features and try running only built-in Defender which gives adequate protection, best Windows performance, least issues, and is from Microsoft who knows how to protect their OS best.
After uninstalling antivirus in Settings > Apps > Apps & Features, restart the PC, then type Security in Start Search, open Windows Defender Settings, there and in Windows Defender Security Center fix anything that's flagged.
If you want the best on-demand scanner install run Download and install Malwarebytes from https://www.malwarebytes.com/mwb-download/
In it's Settings > Protection > Scan Options enable Scan for Rootkits.
Then on Scan tab choose Threat Scan and Run Scan.
Clean up anything found, restart PC and then run again until it comes up clean.
Next check for damaged System Files: https://www.lifewire.com/how-to-use-sfc-scannow...
If it cannot repair them see Step 10 here to continue: http://answers.microsoft.com/en-us/windows/wiki...
If you want to keep Malwarebytes as an on-demand scanner then you can disable its Real Time trial version in it's Settings > Accounts tab.
I hope this helps. Feel free to ask back any questions and keep me posted. If you'll wait to rate whether my post helped you, I will keep working with you until it's resolved.
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