National Credit Adjusters bushwacked out of accepting settlement that was offered. took my money!!!! Hutchinson, Kansas

In Feb. 2010, i was mailed a settlement offer from National Credit Adjusters. The account was for $ 420.00 originally and was settled for half. $ 210.00.

i am working hard at clearing my credit as you notice it was tax time and i had the money to take care of this. The offer expired on Feb. 26/2010.  i called them as the letter states on the first line and submitted a check on the 5th for the $210.00. 
they cashed my check on the 9th of Feb. i called to get a confirmation receipt letter and was told that my money was excepted only as a payment on my account, because i did'nt call first. representative claims she could not find my phone call. what does that mean? i paid on time and you made a deal.

third phone call as of today 4/28/10. i was told that the other 210.00 balance is now sold to another credit collector. This is obscene. I paid. They offered. Clear my debt.!!!