SPRINT SPRINT refers bogus bill to collections 4 years after account closed Richmond, Virginia

In June of 2009, I settled my account with Sprint and closed it since I was leaving to work overseas the next month. I had received a final statement showing a -0- balance. Now, 4 years later while still overseas, my sister sends me a scanned copy of a bill from a collection agency on behalf of Sprint demanding settlement of my balance for $202.47 but will gladly accept $101.24 until March 2013. This is outrageous. Do I still have a copy of that final bill of 2009? I doubt it. I wonder how I should handle this. I've been told if I call Sprint, they will advise me to deal with the collection agency which certainly will not be sympathetic or informative since their sole objective is to make money. Should I contact the Labor & Consumer Affairs Complaints Division in Washington, D.C.? Someone suggested I pay this small amount but what is to prevent them from doing this again? As a matter of principle and knowing I settled all my final bills before departure, I am not handing over $100 of my hard earned money. Advice anyone?