How to block a lost American Express credit card immediately?

I've been a customer for 6 years. The biggest upside is the customer service. The biggest downside is the slow mobile app. If you do most banking on the app, test the app at a branch before applying — it's surprisingly old.

Credit score impact: each hard inquiry (which happens on card application) drops your score by 5-15 points temporarily. Applying for 3 cards in 2 months is fine IF you get all 3 approved. If 2 get rejected, you've taken a hit with nothing to show for it. Apply smart, not fast.