Can't activate answering machine

I have a Siemens Gigaset S455 SIM. The manual does not come in Enlish, and I can't figure out how to activate the answering machine. (I was able to change the display to English, so it does not match the pictures in the manual!) I am able to record a voice message, and I check the box saying "answering machine", but when I call it it just rings. Then, when I check the settings again, the box is unchecked again.