May I just ask if that's an iOS or an Android device? Just make sure to check if the serial number listed under the Trend Micro Mobile Security app's Settings is the serial number that you currently use; that would mean it's already activated. The serial number may start with letter "X".
The entry that expires on the 24th of November 2017 you see on your Trend Micro account might just be a trial version.
We'll wait for your reply. Have a lovely weekend! :)