Why does my iPhone use my location when I tell it not to? Why does my iPhone use my location even though I tell it not to? As you can see from the Time Zone setting, I have it switched off, yet it says that my location was recently used. Why bother having a switch at all?
This is a known defect that started with iOS 10.3.  Dozens of Apple fan sites, including Apple's own discussion forums, are filled with people complaining about the bug.

According to some people on this Apple discussion forum, Apple is now considering this 'expected behavior' and doesn't have any plans to fix it.  I'd take that with a grain of salt because it's just one person saying they were told this by an Apple support person.

I'd recommend you file a bug report as well as provide feedback about your displeasure.