Please take the time to understand this, as I cannot fathom what is causing this issue.
My Mum has a postpaid account with Telecom, and has been having this issue at least once a week.
At the advice of telecom NZ, she has bought a new phone, swapped sim cards and all the usual resets.
Just to be clear - this is not user issue (proof below) , this is not an issue with the phone, this is an issue with Telecom service.
Problem:
Message One: On the 10th April, Mum sent an SMS to her friend. No issue.

Message Two: On the 23rd April, Mum sends another SMS to the same friend. It looks fine on Mums Phone.

Message Three: This is how mums above message appears on her friends phone.
Half of the message is sent correctly, then for some reason, it is truncated.
Message one has been inserted into the message that mums friend receives. This only shows on her friends phone, mum is oblivious to the fact the message she sent is not the same one that her friend receives.

This is the strangest thing I have ever seen.
Mum has been into telecom three times. They keep saying it is a phone issue, so mum bought a new phone.
Then they said it was a sim issue, so mum got a new sim.
Then they said it was an issue with her friends phone, however this happens to alot of people on mums contact list.
I have reset, updated everything.
At a complete loss :-(
Thanks for reading.