I'm disappointed in your behavior.

[svetlana14]

Are these phrases and sentences colloquial? The idea is that a business partner is frustrated by the behaviour of his counterparty.

• 
  
• British:
  
  • I'm disappointed in your behavior.
  • I'm not happy with your recent actions.
  • I'm concerned about your recent performance.
  • I'm not sure I can continue working with you if this is how you're going to behave.
• American:
  
  • I'm let down by your behavior.
  • I'm not pleased with your recent actions.
  • I'm worried about your recent performance.
  • I don't know if I can continue working with you if this is how you're going to act.

 

[emsr2d2]

I'm not sure why you've separated them out into British English and American English. The only one I wouldn't use (in BrE) is "I'm let down by your behaviour". I don't find it natural at all. I might start with "I feel [very] let down ..." but not with "I'm". Also, if the two lists were supposed to reflect meaning, I wouldn't say that "disappointed" is the same as "let down".
I would use the other seven sentences.

Note that you misspelled "counterpart".