did you only connect the pins to Vdd or also with the resistor to GND? I think without the GND connection there is no current flow to detect for the ST chip so this wont work.
You could do like this with a keydetection that detects the voltage level on the key pins like this chip www.austriamicrosystems.com/AS1115
but on the ST chip I guess you need the resistor to GND to get it working. (Unfortunately the ST datasheet doesnt explain in detail how it works, so it is just a guess)
Additionally be careful for too high capacities on the key lines, this needs time to discharge before detection works.
For the DIgits not working: See page 22 section 8.3.1 of the ST datasheet