Even though you have automatic updates turned off, the new IOS update it’s already in your phone or iPad right now waiting for you to complete the install. It’s not yet installed but it is sitting there waiting for you to tap to install. So if you want to disable this reminder do the following:
1. Tap on the Settings icon. Then on General.
2. Tap on “Storage & iCloud Usage”. It might just say Storage on your device. When the next screen appears you’ll see on top the word Storage. Immediately underneath you’ll see Manage Storage. Click on it and wait until the list of apps is fully populated.
Depending on the amount of apps you have installed it can take up to 30 seconds. Look through the list till you see the iOS update. Tap and Delete it.
The pop up notice should be gone. No need to worry about loosing the update, you can always get it later. If in the future you get the pop up again, simply repeat the above process all over again.