Download an app called anti adware in the Play Store buy Keerby. It's an orange icon. Once you install it go in and click scan for viruses and it will bring up all the apps that you have installed yourself that are threatening and cause ads to pop-up you need to uninstall all the ones that you installed. Especially the ones in red. Do not uninstall the apps that came with the phone like Instagram, and voicemail, it finally got rid of 99% of the popups on my S9 Galaxy. Good luck. It worked for me. And it's free.
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