Which one you received? Try the other one (COOL15) and it may work.
Also, there is a bug with Freecharge. If you have signed into another Freecharge account using some other app / web browser in your phone (say for payment at other sites (eg: dominos), then Freecharge gives you notifications for that account too on your phone, even if your Freecharge App is not signed in with that account.
So, if you received the notification, it is some other account of yours which was used on this phone. Try your luck.