Did you provide evidence that you were out of the country? By the way, I have had a debit card mailed to us activated as well and know how you feel. Luckily I received it, but a heads up that it was coming and a heads up that it would be mailed activated would have been nice.
Odd....I've had many, many cards (both credit and debit) mailed to me over 30+ years. From USAA and other companies. I've never seen nor heard of an activated card (both credit and debit) sent in the mail. All cards come with that annoying little sticker that provides activation instructions. It's true the activation process would be simple to execute unlawfully, but the nefarious little jerk would have to have sensitive information to do so. USAA moderators: is it possible USAA fouled up this weak? As for proving you are overseas related to a credit card issue, the last time we went "overseas" (rather than just in Cancun ot Puerto Rico), USAA fouled up on the side of fraud protection. When we landed at JFK frolic Belgium, as I switched my phone's card from a Europeans to USA card, I found a note from USAA informing me they were deleting that Visa card as I had European transactions on it. Stopped them immediately with a call. An angry call! Doing so would have stranded us in Europe without the means to buy food/gas, hotel rooms, and tourist trash. And yes, I had notified USAA in advance we would be in various countries (I listed countries we dedn'yt plan too visit in the off chance we might go to unlisted countries. USAA fouls up very often, but sending activated cards? Doubt it. Tchuss!!
Not sure I'll ever convince you, but yes, my wife's debit card was sent through the mail activated already. I knew it was coming because we asked for a new one, but when the card came in, there was no sticker, I went online because like you, I had been used to the sticker to activate and online everything looked like it was activated, so I called USAA. I was told by the customer service rep, that yes we send it activated for your convenience, when I asked if the card was ready to use. I was shocked because I was never led to believe it would come that way. Now maybe they have since changed their ways, but be warned, if you order a replacement card, be sure to check online where you can block or activate your card, because chances are it'll be active.
Contact the Consumer Financial Protection Bureau. It is a Federal Goverment ( Non-partisan and Non-funded by Congress ) agency. They are self funded by the fines they recover from buisnesses. If you are not satisfied with the response / answer from USAA contact them to help you.