Anonymous Group Texting

I have been sending daily text messages each day on my iPhone 6 to a group of 100+ people as SMS messages, which ensures that none of the recipients of the text can see who else is on the text list. Once iOS 11 was installed on my iPhone 6, however, it will not allow me to send the message to this group without enabling iMessaging. When I enabled iMessaging and sent out the text, I was notified by my fellow iPhone users on the text list that they were able to see all the other people who were part of that group text (which I do not want to happen). How can I continue sending group texts to everyone without people being able to see who else is receiving a text?

Thanks!