A few years ago, when I paid by check, my Shell gas card did not post my payment until the day after it was due even though I sent it a week before it was due. I got dinged a little over $4.00 in interest. I didn't get that mad, but I got even. I sent them more than I owed and for the next few months they sent me a statement with a credit balance. In January, they had to cut me a check and mail it to me. I would have kept doing this for years, but I cut up the card earlier and never used it again. I figure I cost them more than the interest they charged me.