Looks like the basic functions of the phone are correct. Remain the answering machine. Are you sure it can act as an answering machine?
If it can act as answering machine the reason it is not doing so may be the following.
- Answering function is turned OFF
- Answering function may be ON but the number of rings before it answers is set too high.
I suggest you try the following
Call you phone. Let it ring at least 10 times. If it can act as an answering machine it will pick up the phone and read the welcome message, because most answering machines (the recent ones at least) answer after 10 rings even if answering function is turned OFF.
The phones that can be answering machines usually do have a display that shows the number of incoming messages, or a LED that flashes to let you know that you have new recorded messages.