That is correct, you cannot payoff a loan with a credit card. There are several reason behind that. First, you could dispute a charge up to six months after payment. By that time MVCI would have removed their name off the deed as the lien holder, causing a huge mess. Second, the vendor fees for processing cards is anywhere from 3-10%, while paying monthly the interest helps offset that cost.
In terms of making monthly payments toward your loan using a card, that was a promotion run my MVW for financed contracts dated January 2, 2014 or later. This promotion allows the owner(s) to pay their loan via Automatic Credit Card transactions regardless of the owner living domestically or internationally. This was only for the normal monthly amount, nothing extra to principal.
Even for international owners, they still have to make their final payment via a check in U.S. funds, or wire transfer.