Oh my...I'm sorry for this to have happened to you - but......
good for you demanding to see the original agreement. They seem to be quite unorganized.
It's possible that they can file suit, and perhaps contact the district attorney's office, file a report for theft....however, they have to prove same - and it seems that they don't have any evidence to date. If they file suit, they would need to attach a copy of the signed agreement to substantiate their claim - otherwise it's looked upon as a frivolous lawsuit.
Important: You must protect your rights - therefore, you need to document each and every time you called this store concerning this incident, and hopefully, you recall the names of all store employees that you have dealt with and you need to document their names and, you need to send them a letter, via certified mail, return receipt requested, and advise them of all action that you have taken to date in which to remedy this matter. State that you were under the impression that this was an agreement for 1 year - that you have paid in full, according to your belief and knowledge...that you paid timely during this one year period - and that if they can show proof that you do in fact owe more monies...that it was for a 24 month period of time (and total the amount), that you will gladly pay....however, due to their inability of proving to you that there is an extended agreement, you do not feel that more monies should be forwarded to them at this time....Emphasize that you will gladly pay if monies are actually due but that you are only asking for them to show proof beforehand. Ask them to please contact you within 15 days from the date of the letter in order to resolve this matter. Send this off as stated, certified mail, return receipt requested......keep a copy for your records...and don't misplace it!
This letter will prove invaluable should a lawsuit be filed - or the matter turned over to the district attorney's office...and should they take such action, I suggest you contact an attorney immediately.
If you have any further questions, please let me know.
Please take care.
Peace, Love & Happiness,
The Mystic Wave