Citifinancial Retail Services Charged interest on entire amount beause last payment was received 2 days late Tempe, Arizona

In August, 2008, I purchased a temperpedic bed from Brookstone, Santa Barbara.  At the time of purchase I put $500 on my credit card and financed the remaining balance of $2268.10.  I mailed the last payment on August 25, 2009, which turns out to have been the due date.  Yesterday I was floored when I received a bill in the amount of $373.94, which turns out to be the interest and other charges on the total amount of the loan because they received my check two days late.

Today I spoke with 4 different individuals, all of whom told me the party line of there is nothing we can do.  I had to fax a letter explaining the circumstances to the Resolution Department - they will not take phone calls. 

In the letter I explained that I had fractured my shoulder in 4 places on June 28, was in a sling for 8 weeks and in awful pain.  In fact, I am still taking pain pills and undergoing physical therapy.  After several more treatments my insurance will not cover physical therapy, so I will have to pay out of pocket.  Further, I am on a fixed income and because I lost $600 of income since April, I clearly do not have the ability to pay almost $400.