Just switched from iPhone 5s to iPhone 6s and I'm unable to listen my music without Wi-Fi what to do?

Also switched from AT&T to T-Mobile if that matters at all. All of my music was purchased on iTunes. Music is on my the laptop iTunes. I didn't turn on the Wi-Fi use only for music whatsoever.

T-Mobile sucks. It is possible that i is their fault. I've had bad experiences from them. I don't know too much about Apple though, sorry I couldn't help with that.

Your music isn't synced onto the phone. You can download by looking at your purchases in iTunes.