Hello martien10,
Welcome to Apple Support Communities.
We understand that virtual voicemail isn’t working as expected. We are happy to help.
Does your wireless carrier offer virtual voicemail? We are asking because this is a carrier feature.
Please try the steps here as they may help: Check your voicemail on iPhone - Apple Support
"Set up voicemail
The first time you tap Voicemail, you’re asked to create a voicemail password and record your voicemail greeting.
- Tap Voicemail, then tap Set Up Now.
- Create a voicemail password.
- Choose a greeting—Default or Custom; if you choose Custom, you can record a new greeting."
If no resolution, please contact your wireless carrier.
Let us know if you have further questions.
Take care.