Pop up ads on my Galaxy S8+?

All of the sudden I started getting pop up ads on my phone. They occur at any time, not just on line or in certain apps. They are extremely annoying and interrupt game play or video streaming. I cannot figure out where they re coming from. Any advice would be lovely. Also, they have an "opt out" link but when I click it, it asks to download an application or enter in my phones IMEI, MEID, or ESN. This seemed awfully fishy to me so I have not done that.