Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
What you are describing is a well known scam.
This is an illegitmate threat by an illegitimate company - they are trying to take over your computer. At best, they'll charge you for their help and try to steal your personal information, at worst they'll do that as well as hold your computer hostage until you pay them hundreds of dollars to release it.
You should immediately disconnect your computer from the internet connection, and run antivirus and malware software. If you aren't comfortable doing this, take it in to a pro, locally.
You need to make sure all traces of any software they used are gone, or they'll continue to have access to your computer, monitor your activities, access your banking info, etc. No legitimate company would initiate a call to you via phone like this.