Change from 12h time to 24h time on my iPhone not working properly

Hi there,

I have an iPhone 6s and ever since I've been updating to the latest iOS 11.1.1, I've been having issues with my time clock.

My time is set to 24-Hour Time (Settings > General > Date & Time), my clock is changed to 24h BUT all the apps that use time such as Calendar, Clock, Mail, etc are still set up to 12h time which is very frustrating, since it used to work perfectly before the iOS 11 updates.

There no other option I can tick on each apps to change the time so what to do?
I hope this issue will be fixed soon.