I don't blame you at all, CanadianGran, for being extremely annoyed at the disruption to your planned Book Group meeting. It is very bad-mannered to change a meeting at such short notice, simply because people haven't bothered to read the book in time. The problem lies in the fact that Book Groups are informal organisations; the meetings are usually held in places where it is not necessary to book or pay for a venue, and, to put it delicately, include members who are, um, used to controlling events in their own households and don't always consider the needs of others.
It is also hard as members are friends.
I have been a member of a large book group for many years, and these sort of challenges have arisen, usually from the same few people who don't want to miss meetings but are not prepared to compromise on their own arrangements.
I would join in the texting discussion but just reiterate without acrimony how much you were looking forward to discussing the book, as you had suggested it, and the fact you had booked time off from work because you wanted to hear the opinions of others. It sounds as though some members have realised what they have done, so grit your teeth and hold hard to your line without losing face.
Hope the meeting goes ahead.