HSBC - Nautilus - Did not apply payments to our account Carol Stream, Illinois

Back in 2004 or 2005 my husband called these people, got a credit approval over the phone, and ordered a BowFlex.  We love the machine itself.  We have made consistent monthly payments via automatic transfer from our bank, despite the fact that we have not received statements since we left Florida, even though we changed our mailing addresses each time we moved. By my calculations we have repaid them $2,300 on an $1,800 loan.  They are claiming that we still owe them $1,100 and that the last payment they received was 2 years ago or so.  I'd sure like to know where all the money we sent them went because I sent them out via our banks' electronic bill pay and the funds were always deducted from our accounts.