[Drolefille]

You should be able to specify something like the above or make sure you write "Extra to Principal" on your checks. You can even contact your company and ask how this should be done. This should ensure that your payments are applied appropriately. (Disclosure: I work at a bank and am familiar with loan files, but things may work differently elsewhere)

Banks/Lenders are in this to make money. It's not surprising that they're going to pay off your interest first if they have a choice.