You are not the only person this is happening too. There is another post or other people are commenting on the same thing. Here is the link to it. https://communityforums.rogers.com/t5/Account-Support/charged-for-unknown-us-text-messages/td-p/498949
This just happened to me today.14 messages that I sent on WhatsApp to a US number being charged by Rogers.I understand if my Wi-Fi is down that could possibly happen. My Wi-Fi is rarely down BUT 14 times in a row is basically impossible.