@dopeo: Please try restarting your phone in Safe Mode, as this will disable all third party apps, and help to verify if the pop-up adverts are stemming from an external source. To enter Safe Mode, press and hold the Power button until the 'Power off' prompt appears on the screen then release > Touch and hold Power off until the 'Safe mode' prompt appears then release > To confirm, tap Safe mode.
Monitor the device for a few hours, depending on the frequency of the pop-ups. If you notice an improvement, restart your phone as you would normally, and uninstall any apps that you have introduced to the device since you first encountered the issue. As it isn't possible to determine exactly which app is at fault, I recommend approaching this via a process of elimination.
