Hello all:
Well, I am happy to say after sending the C&D letter to Sonic and explaining how my extension payments (here in Ohio) should be applied to my principal balance---they AGREED! They deducted the amount of my extension payments and only charged me the bank charge of $20 AND are allowing me to make monthly payments with a money order.
With zip19 (aka Northwest...), they are still not providing me with a U.S. address just the Malta one. I did call their e-care centers and spoke to a nice rep. I asked him to provide me in writing were to send the legal amount owed.