I have an iPhone 6s and just switched from Sprint to T-Mobile. Since the switch, every SMS text message I send shows as “not delivered” on my end, but the recipient gets it three times. This does NOT happen when I text another iPhone user and it goes through as an iMessage. I’ve spoken to customer service at both T-Mobile and Apple, and neither were remotely helpful.
I’ve restarted the phone, I’ve adjusted the text settings per T-Mobile’s instructions, I’ve tried it on wifi and on the network. Nothing helps. From Googling, it looks like people have had this issue in the past but I’ve never found a solution. PLEASE HELP!!!