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If you stopped making payments early, and did not make any payments to principal, then most likely, yes you do.
The only way to determine whether or not you owe anything is to get a full accounting of your loan. The plaintiff should provide this documentation to you. If they have not provided it to you voluntarily, you should ask them for it (ask them both in an "Interrogatory" and with a "Request for Production of Documents" (civil discovery) so that you can review the accounting, determine if their accounting is accurate, and see if there is any error).
If there is an error you may be able to settle the account short of trial.
I do recommend trying to push these matters in to mediation before trial if at all possible, it gives you an opportunity to settle the case without having to go to the time and expense of trial, and may give you an opportunity to pay for less than the full amount demanded (if you go to trial and lose you will end up paying the full amount plus their attorney's fees - I assume that your contract has an attorney's fees agreement in it). Contact your local bar association and ask for referrals to local mediators (you can also ask the court about mediation programs they may have that would work for your case).