Missed a call from this unknown number on 30 September and the caller didn't leave a message. I don't usually respond to these but as I was expecting a call I rang back in case this was the call I was expecting. My call was not answered but a text message arrived immediately stating: "Done". This was extremely suspicious looking so I texted back: "Done what?" The texted reply was: "Sorry. Pushed the wrong button. Was in a phone call and had to reject the call. Thanks.". The caller never identified him/herself in any way and has not attempted to make contact since, making all this seem pretty suspicious. I am going to block this number and screenshot, then delete, these messages.