Hi wilber_force, thanks for your post - sorry for the delay getting back to you.
I'm also sorry to hear you've encountered this problem when trying to send text messages.
Further to enlli's suggestion above - many handsets will convert longer text messages to MMS messages automatically, and group messages too if you're sending to more than one contact at once. This would need to be turned off in the handset's settings.
If this continues after you've checked the settings and everything seems correct based on the above please let us know.
Things seem to have stabilised once I found the setting that is only against my wife in the messages app about sending SMS and MMS messages. No idea why it is just against her, I've not seen it against others, not really looked at many contacts, all a bit weird.