I think you will need to enable rSAP mode on the phone to get messages etc. to appear on the MMI. The default config of (later) Android phones is to only enable bluetooth headset profile. This is where the phone "owns" the SIM and all calls/messages are done through the phone. rSAP allows the phone to export the SIM connection to the car so the car becomes the phone. It is possible (there is a paid-for app which enables this on the Play store). The plus side is if this is enabled, you get to use the cars aerial, so tend to have a much better signal. The downside is that in rSAP mode, any calls/messages end up on the "car phone" (i.e. MMI) so when you take your phone out of the car, there is no record of calls/texts on the handset.
Or at least that is how it works in my Skoda Superb that has the RNS510 head unit....