Call Monitor Sensor not shown - FRITZ!Box 6591
**Describe the bug**
The Call Monitor Sensos will ot appear in the Home App as well as I can't see them in the Homebridge Config UI

**To Reproduce**
Steps to reproduce the behavior:
Enable the call monitor

**Expected behavior**
No sensor shown

**Screenshots**
![image](https://user-images.githubusercontent.com/105149/122197897-ef4bb880-ce98-11eb-89d9-13f11637d167.png)
Username & password removed for security reason

**Desktop (please complete the following information):**
 - OS: Windows 7
 - Browser Chrome


**Smartphone (please complete the following information):**
 - Device: iPhone 12 Pro MAX
 - OS:  iOS 14.6


**Additional context**
I also tried to use the call monitor without country-&cityPrefix without success. Call monito was enabled by `#96*5*`