Residual Interest

On February 26, 2010, I made a final payment to my FIA Card Services Credit Card for the amount of $10,106.91. This was the TOTAL AMOUNT that was due on my statement. After making the FINAL PAYMENT of $10,106.91, I assummed that I had paid off the total balance that was due and that my account was at a ZERO BALANCE. On March 17, 2010 I received a bill for something called "RESIDUAL INTEREST" for the amount of $54.69. How can this interest accrue when I had already made the final payment on February 26, 2010 for the entire amount on my statement well before the due date? After making the entire payment of 10,106.91, the balance should have been 00.00. What is "RESIDUAL INTEREST"? As far as I'm concerned, this is nothing more than a SCAM! When a consumer receives a statement for the total amount due, and pays that total amount in full before the due date then why isn't that consumer's balance left at $00.00. This makes absolutely no sense to me! I went ahead and paid the amount for RESIDUAL INTEREST OF $54.69 then I filed a complaint with the Federal Trade Commission and the Better Business Bureau to investigate this and thousands of other complaints against FIA Cards Services! This "RESIDUAL INTEREST" is nothing more but a way for credit card companies to reek millions from consumers!