And "other people" refers to *all* the different networks I assume.
Before getting on to the service providers' customer services can you borrow different mobile handsets in order to try a few tests ?
You could swop your SIM to a test mobile, your friend could do similar, and then if the text gets through you have a working situation. If not, then the problem doesn't seem to be handset related and you need to complain to the service provider.
Then one of you, maybe you, could swop back, retry to send the text from your original handset and see if it gets through. If it does then your handset seems probably ok, if not then your handset is suspect.
Then change it the other way around, you swop back to your test handset, your friend swops back to their usual one, and you retry to send the text. If it gets through then your friend's handset seems probably ok, if not then your friend's handset is suspect.
If you can do this it gives you confidence as to where the issues are, and plenty of evidence to tell the service provider if it seems to be their network data with a problem.