Fritzbox 7390 and Samsung Galaxy S5

I have a Fritzbox 7390 modem now. The first few days, I could get all the calls routed through the modem to my mobile phone, but I do not get them now. I have tried to contact Fritzbox, but their response did not lead to any resolution of the problem. What settings do I need to get the calls also available to my mobile phone? Many thanks. I have installed MyFritz, Boxtogo Free and Fritz Fon apps on the mobile.

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8.1 Pro with Media Center, 64 bit
Processor: Intel(R) Core(TM) i7 CPU Q 720 @ 1.60GHz, Intel64 Family 6 Model 30 Stepping 5
Processor Count: 8
RAM: 8125 Mb
Graphics Card: AMD Mobility Radeon HD 5000 Series, 1024 Mb
Hard Drives: C: Total - 239656 MB, Free - 203998 MB; D: Total - 236929 MB, Free - 135959 MB;
Motherboard: Hewlett-Packard, 1449
Antivirus: Windows Defender, Disabled

Samsung S5: Android version 5.0