Why did I just get a check from the US Treasury?

It looks like a legit check. It's only for $13. It also came with a little order form to order a 2008 Eagle Silver Proof Coin from the US Mint.

It says "Opana Kans (Kansas) Cytax Refund" on one part of the check. What is this?

Silver Eagle Proof Coins Ending Soon on eBay:
1990-S~NGC PF 69 ULTRA CAMEO PROOF AMERICAN SILVER EAGLE~1ST YEAR~~BETTER DATE

US $104.95 End Date: Tuesday Feb-07-2012 6:28:22 PST Buy It Now for only: US $104.95 Buy it now | Add to watch list

• eBay Ending Soon:

  1994 AMERICAN SILVER EAGLE PROOF DOLLAR US Mint ASE Coin with Box & COA $105.95 4h 43m

  2006-P Silver Eagle - REVERSE PROOF NGC Proof 69 - PF69 $255.00 22d 14h 37m

  1986proof, 2010 proof, 2008 uncirculated, (3) 2010 uncir.2011 silver round eagle $240.50 6h 10m

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