The problem being I got a phone call and they accessed my laptop and now I have turned the wi fi off because they obviously have access to it. I need in simple terms how I can erase or get rid of this problem
Honestly if it was me, I would make sure that WiFI WAS OFF (Like you said it was.) and then wipe the system completely of any and all data.
Of course this is assuming that you have a backup of your files previous to the hacking. If not, well then it gets complicated figuring out what files are safe to use.
So to wipe the Mac, boot it up while holding CommandR until you see the white Apple logo on a black screen.
When you get to the macOS Utilities screen, select disk Utility from the Utilities menu. Select your hard drive on the left and click on Format.
This will erase EVERYTHING on your drive
Once that is done quit out of Disk Utility, connect to your WiFi, and proceed with macOS install from the main menu.
This will likely install the version of macOS that your Mac shipped with. You can upgrade it for free once you have done this installation and restored your files from backup.
Nessie: Change your user password immediately. While logged into your account go to
System Preferences, Users & Groups and click the Change Password... button.
Examine the list of other users, too, and delete any user account which you do not recognize. You will need to click the lock at the bottom-left of the window to delete other accounts, and your account must be an admin account.
Malwarebytes is one utility to start with to scan your Mac for any software the scammer has installed. You'll need to download the software onto a USB key on another Mac.
Please read this site thoroughly.
Steve Chambers advice to wipe the HD clean is the best method to clean this all up, but can be a daunting process.
Report back with your progress. We're here to help.
The problem being I got a phone call and they accessed my laptop
How, exactly, did they do that? It is exceptionally unlikely that an unknown random person got into your laptop all by themselves. "Pay us or we delete your data" is called "scareware".
Did you install a program and let them access your laptop? That's your fault.
What you do now is restart your laptop in recovery mode (press command-R at power-on) and restore it from the Time Machine backup the day before this happened. You will lose everything you have done between then and now.
If you don't have a Time Machine backup, follow the instructions from Steve to get a clean system again.
And next time a random person calls about a problem with your computer, just hang up.