"Sorry, I did not hear what you said."
Translation:Beklager, jeg hørte ikke hva du sa.
Desverre means "unfortunately."
Unnskyld and Beklager are a little more vague, but typically Unnskyld is used when you are apologizing for something that was directly in your control, while Beklager is more common when something is out of your control.
For example, you're more likely to say Unnskyld when you are apologizing for breaking something. (ex. "Unnskyld, jeg ødelagt bøkene dine.") But you would typically use Beklager when apologizing for something like not having a product at a store or if a place is closed. (ex. "Beklager, vi stengte klokka åtte; klokka er ti over ni nå.")
Hope this helps!