iMessage not working on IPhone

So iMessages aren't working on my phone. They just show green. But they do work on my laptop from that same number. I also moved the sim card from this phone to another phone and it didnt work on the other phone. I then went to t-Mobile and they gave me a new sim and that didnt work. I also factory reset the phone and that didnt work. I also turned on and off a bunch of things on both my mac and iPhone and that didnt work. Any ideas? Thanks!