Reply to a Message

I switched mobile carriers from AT&T to Cox yesterday, and use an iPhone. When I was with AT&T, if I wanted to reply to a specific post within a text message thread, regardless of whether it was a group or individual chat, I would press the post on my phone screen and hold it down for a second, and a drop-down menu would appear with "Reply" as the first option. After I switched to Cox, the "Reply" option only appears if I'm responding to another iPhone user; it does not appear if I'm responding to an Android user. There was no distinction when I was with AT&T; I could reply to anyone. In my Settings, both RMS and iMessage are turned on. Why does Cox not allow iPhone users to reply directly to a text message sent by an Android user?