AdBlock for Mobile by BetaFish (that's us) doesn't use a VPN. Several of the 500 or so other ad blockers in the App Store do. Many of them are named "Adblock" or "AdBlock," and some of those even have logos that look a lot like ours. We report them to the App Store when we spot them, but they're quick and shifty and it's hard to keep up.
Look in your apps and uninstall any that seem to have something to do with content blocking and have a logo that looks like the one in the message you're seeing. Another way to try to find the culprit is to check Settings > Safari > Content Blockers for the name of the app. If that doesn't help, you may need to contact Apple Care.
By the way, if you were looking for the real AdBlock, here's a handy link to AdBlock for Mobile in the App Store.