Alas, I am truly sorry to say this; however;
There are a hundreds perhaps thousands of fake virus notifications floating around right now. They claim that your device has been infected and they try to get you to get their various products, as you say (real or not), such as VPN or Virus Software. They are lurking just about anywhere you surf and as best as I could research there is not much that anyone can do about it now. They are after your hard earned bucks and will keep coming no matter how hard you fight back. It depends on how much of your time that you want to spend blocking them, just remember that they will always come up with a new IP address etc. just like telemarketers steal phone numbers.
AD Block extensions on a desktop helps some, not much helps on an iPhone.
Then you get websites that whine about you using AD blockers or will not let you access them because you do. Catch 22. If they won't, then I figure that they are not worth anything to start with.