Oh god Ness - I go through this every dame day.

i have tried being nice but it only gets you so far and then the teachers/career has ended going back to what they think is best. grrrrrrrrrrrrrr.
I tell the teachers/career that my child's name is eg Wilhelm not Will and I WANT you to call him by his name not to what you think he should be called. It is who he is and later in life HE can choose his nickname...so right now we call him by his NAME

its a bit harsh but it gets the message across and its worked for us.

I find it so frustrating when people think their being 'cute' when they are so obviously being annoying!

If all else fails miss say their name and see what they think when you ignore them