Hello Jakahole,
Welcome to Apple Support Communities!
We want to help get your messages sending without any issues. Try the steps here first for an issue sending messages:
"If you experience issues like conversations in Messages showing up as separate threads or sent messages appearing as green message bubbles instead of blue message bubbles when you set up a new device, update your settings using the following steps:
- Update your device to the latest version of iOS or iPadOS if needed.
- In the Settings app, tap Cellular. Make sure that your phone line is turned on. If you use multiple SIMs, make sure that the phone number you want to use is selected and turned on.
- In the Settings app, tap Messages. Turn iMessage off and then back on.
- Tap Send & Receive.
- Tap the phone number that you want to use with Messages.
If you have issues when you try to receive a FaceTime call after you set up a new device, you can also update your FaceTime settings."
This Apple Support page has the full details: If you can't send or receive messages on your iPhone or iPad - Apple Support
If it only happens with SMS messages, you'll want to reach out to your carrier again.
We hope this helps to further isolate and resolve the issue.
Cheers!
