McAfree pop ups on Macbook Air

I keep getting system pop ups to say that McAfree is about to expire, there are 5 viruses on my MacBook, PC is at risk etc. I don't have McAfree and I know this can be a scam - so I have bought the AntiVirus One app to check my MacBook and hoped this would remove the pop ups too.There are no virus or anything on my device and I also have an Ad blocker on my browsers, yet not matter what I do I still have this pop up every 10 or so minutes. it then stays on my control panel.

I have cleared cache and cookies from all browsers (Safari, Chrome and Firefox), I have updated the MacBook, and have searched apps/files for any McAfree items.

Please can someone help me get to the bottom of this, hopefully without having to reset my whole computer.