Huge hit to credit score

WOW, I had read that it might affect your credit score. Mine went from 850 to 698, only change was I used affirm to finance a new phone. I thought what the heck, 0% financing sure. I should of just paid cash or credit, well now I know for next time. NEVER use affirm if you don't have to! I checked 10 days ago ( credit score 850 ), and just this morning (698) , and to top it off I changed my mind about the phone and sent it back, so now I have a lower credit score and NO new phone! Oh well ... Lesson learned.