Okay, here's SOMETHING
WCPO -- How to stop 'congratulations' ads on your iPhone
A quick news video worth watching at that link explains most of this all pretty fast.
If you do a basic google search for "congratulations amazon user pop up ad
" you'll see that these pop-ups are all over the interwebz, and that they usually aren't directly the fault of the website you might be on when they occur.
Advanced "browser hijacking" malware is on your phone (from somewhere) that takes advantage of frequent weaknesses in many websites to "launch" and do its thing.....)
Lots of specific directions on the web as far as how to fix it on your own phone. And from the sound of it.....
YEP, REALLY....THE PROBLEM IS
ON YOUR PHONE.....you unwittingly downloaded it somewhere......it could be any number of sketchy apps you've acquired (or search engines)....
Time to do some app/browser history housecleaning and setting changes.
Additional instructions on that new website that can help fix it.....and all without resorting to an outright ad blocker --- there are "pop up blocker" features built right into Safari on your iPhone that you can activate.