How do I resolve this?

A bill from July 2010 for $43 I never received. Finally I was contacted for the first time of this charge and it was from a collection agency in the amount of $227. This was Jan. 2011. The fee was settled upon and paid the same day. My concern is due to a Post Office mishandling I never received a I'st second or third notice, as well as no phone call to request payment. My concern is the effect this error due to no fault of my own will have on my credit score. Can you suggest?