I have my loan serviced with Green Tree. I have been paying more than the amount due each month that I would expect to be applied to principal, but instead they post it as Unapplied Amount. I have never worked with a less competent services. I 've worked with over XXXX in the past that know how to apply additional payments toward principal. Thus I am paying interest on amounts of principal that I have already paid. This must be illegal. 
