Active voicebox due to iOS Live-Voicemail feature

I’m a loyal Apple iPhone and T-Mobile customer for many years. Recently, it came to my attention, that there is a voicemail service active on my personal mobile number. This is pretty annoying, as I never use voicemail on my private mobile number. Okay, maybe due to an update or something. I quickly found the standard mobile code to disable any forwardings: ##002# is a standard mobile code that cancels all call forwarding on your phone, including when the line is busy, unreachable, or when there is no answer. Surprisingly, this didn’t worked… There was still am active forwarding to a voicemail service, even if I didn’t got any notiofication when someone left me a message on the voicebox. I continued my research and stumbled upon a forum post that mentioned the iOS live voicemail feature. After disabling this feature, there was no further forwarding to voicemail. You can disable this feature under Settings -> Apps -> Phone -> Live-Voicemail -> Disable.