Your best option is to check your current downloaded apps. If there are any suspicious ones that you do not recognize, proceed to remove them. Additionally, check your current extensions in your browser and see if there aren't any ones you do not recognize. Afterward, you can install Malwarebytes on your phone and do a scan, it should detect issues.
The problem with Android malware is that it can encrypt itself. If it is an elaborate spyware or malware, you will have a hard time removing it. After the initial removal steps, I would recommend monitoring your phone for any suspicious activity. Including more pop-ups, increased phone heat and similar issues. If it persists, I would strongly recommend doing a factory reset and changing your passwords. Hope this helps!