Went crazy and tried lots of things
What I did
1. Called my (voice) voicemailbox.
2. Listened to all messages completely (10 messages).
3. Listened again (just beginning), and deleted one after the other
4. Hang up
5. Took my Phone App in iPhone and moved it from the Dock to a new page in the iPhone (6th or so)
6. Called my iPhone again and recorded a message.
7.
Visual Voicemail shows the record.
Also pushed play button. Worked fine. Also pushed Home button, back to phone App, all ok, turned off all Connections (Airmode ??? in german: Flugmodus), still message in VVM
8. Turned off iPhone, and on again
After that.
Voicemail is still shown and playable, but marked as new again
9. Played message again and again. iPhone turning off and on, always same problem (message marked as new).
10. Called iPhone again. Recorded second message.
Second message won't show up. (Voice) Voicemailbox tells me that I have 2 new messages, thus not the code but t-mobile is telling the iPhone that the message hasn't been played yet / iPhone not telling t-mobile that I did.
11. Deleted first message (the only one being shown)
12. iPhone restart etc. doesn't bring any voicemail entries.
13. Made new call.
14. Now (Voice) Voicemailbox tells me I have 3 new messages, but in VVM the table is empty. (Thus iPhone also didn't tell t-mobile that I have deleted the first message)
15. Started all over again. Didn't work this time.
