Can I be sued for commissions that were approved by three managers and already paid?

I was hired for a position in Sales and was never given a job description nor trained. I accepted the position of Internet Sales Manager because I was doing the job for free for two months because my manager asked for help. I worked the internet based on the verbal instruction of my Sales Manager. I was never given a job description, formally trained, never assisted or monitored. I was left alone with simple verbal orders. I was paid by commissions and verbally told what was acceptable to claim for commissions by my Sales Manager. Although I asked for training continuously, None was given. All instructions and work demands were given to me verbally. After a year of making my commission sheets, I was called into an unscheduled meeting alone with the owner of the company in a conference room who aggressively accused me of stealing money through my commissions. As I sat there confused, I stated I do not understand and before I can finish speaking I was told to “be quiet and do not speak, he (the owner) is doing all the talking and he didn’t want to hear anything from me”. I sat quietly while he pointed out things he said were mistakes on my commission sheets. He claimed they were done on purpose. I was called into that meeting alone with just the owner who never had anything to do with me before who now was threatening me and accusing me. I asked if he would show me the proper way of doing the work and he briefly explained how he had expected the sheets to be done. I apologized and stated I was never explained to do them the way he asked and moving forward I would. He said he doesn’t care, he wants me to pay the money back and my manager had known there was a problem with my commission sheets for three months. I asked “why didn’t anyone tell me they were wrong and show me the right way to do them because I honestly did as my manager verbally told me and I had never done them before? ” I also stated that I gave copies to the Sales Manager and Controller and he (the owner) was also given a copies. How can three Managers check my work and approve it for a year and never once tell me something was wrong or train me to do things right? Can they now demand this money back? I am so confused! The harrassment continued until I had a breakdown at work and was placed on medication from the stress. Going into work was taking its toll because after the meeting they continued to “investigate” me as if I were a criminal and treat me as if I purposely did my commission sheets wrong. Each morning I had to medicate in order to resist a panic/anxiety attack at work. I could not work under these conditions any more. I resigned from my postion and I was told I could not leave the building until I speak to the owner and pay the money back. My arm was grabbed and I pulled my arm away. The owner called me and left a message stating he would give me a chance to come to a financial agreement and pay the money back but i cannot just walk away from owing this money. I am being threatened with a law suit. I refused to be harrassed so I was advised by HR to email a response. I emailed and explained all that took place as I explained here. I explained I was never aware that the way I was doing them was wrong and that noone ever sat with me to explain they were wrong. If they knew I was doing them wrong, why pay me and continue to let me go on for three months after they suspected the sheets were wrong. Please help!