Siri broken on iphone 5 She doesn't understand or mostly not responding at all

First I realized that dictating messages etc. didn't work anymore. Then I tried talking to her and she just doesn't understand anything. Mostly I get no response at all, just the low pitched signal and nothing happens (no Siri dialogue opens, no response). Sometimes when I say 'hello' (loud and clear) she answers that she doesn't understand, but that is very rare.

I can't find anything that helps. I would like some solutions before I reset the phone fully. 

Internet connection is active and working. Siri is enabled. I tried it in different languages. Tried rebooting a few times. Tried turning Siri off and on. Tried resetting  all settings. There is not even a waiting signal, so I don't think it's a connection or server problem.

It used to work perfectly before - can anybody help?