I knew there was something. I called Assurance Wireless several times. Apps would just install themselves, and I didn't even have a google account, or a google play store account. I disabled and/or removed permissions from every possible thing that wouldn't cripple the phone from allowing me to send/receive calls and texts, but still these "instant apps" (or whatever tf they are) kept installing themselves on their own. Sometimes my phone would ring, and I would go to answer it, only to be presented with a full screen ad with a FKNG COUNTDOWN TIMER!! I couldn't answer the phone, or do anything until the timer hit zero, and then I went and removed whatever new thing installed itself. Missed lots of calls because of this. I have uninstalled "Clean Master" alone at least 10 times. I'm appreciative of the phone and the Lifeline service, but really what good is it if I can't answer a phone call?
This is definitely something that came baked into the phone / its software (or firmware). I did not get myself infected by doing something stupid or by installing an infected app. In fact, I have not once even launched a web browser, or done anything
on the internet, except for allowing gboard for speech recognition. I have never installed one single app on the phone, ever. There is nothing on the phone that is visible to me that has the permission to install apps.
Thanks to everyone here for the information and help.