After you file

I've gotten 3 of these letters in the mail in 1 week and another one apparently on the way that went out Friday according to the rep. She also only seen 2 letter were mailed including the one that went out Friday but clearly I'm looking at 3. I've filed the same way for 13years, nothing has changed the only thing I see different is $6.71 on my wages.  I know this might be the reason I was pulled but why 4 letters