I have this too!
I found my phone is lying, my messages are getting through but they received multiple times!
I have restarted my phone (iPhone SE) a few times but no difference.
I am on Tesco Mobile but I don't think that should change anything.
Thanks for reporting issues with the network. As others have mentioned above, we have an official topic about this so we're locking this thread to keep the conversation in one please. Please use this thread for updates and to share your feedback.
The community team.