Why do I have to turn on my data to send, and receive group messages on SMS, on my Mini Droid?

[AC Question]

Every time I am into a group message, I cant send messages or receive messages. In order to see the messages and text back, I have to turn my data on, and turn my Wifi off. The messages come through on the top of my screen, in the pull down. With regular messages I can just click the message from the pull down screen, but with group messaging, if I click the message, it sends me to the area if I would want to send a new message, when I just want to reply in the group chat. Why can't I get group messages just using Wifi? This has been going on ever since I got my phone in February of 2016. This is so aggravating. I have tried numerous places where people could answer this question, and nobody seems to get the right answer. Please somebody help me, Thank You!