Is this in iMessage again?
You'll probably have to ask the school what they were sending and how they were sending it (SMS, MMS etc.).
Doesn't sound like a 48/network issue.
Probably yet another iPhone gotcha like your previous iMessage activation one.
Hope this helps.
I am not a 48 employee - if you need to contact 48 support then please
click here - if the Chat Now option does not appear on that page then keep trying until it does.