stupidcreature hello there. Do you have those issues on user profiles or your owner profile ? Because if it's on another profile than the owner, I'd say you're pretty safe and just have to delete the concerned profile. Because all profiles have their own spaces in memory and do not communicate with each other, they're strongly sandbox.
Although it isn't impossible for a malware to spread out a profile, I'd say very unlikely. So if it is on a user profile delete it and recreate.
If not, you have to know that malware cannot temper your OS because of check integrity with secure boot. And all apps are sandbox and only have access to what user give them EXPLICIT permission. So I'd recommend to delete everything related to the suspicious program and reboot your phone to clean the RAM.
Otherwise, you might have to factory reset your device if not improvements after the following advices.
But wait for other adbices that could be better before hard reset
PS : you can also use the "check integrity" option on security settings to check if some settings have been modified