Why am I paying a huge fine that I didn't comply to?

In 2007, I worked at a close out store as a cashier. In the months I was working there, my friend "Bob" wanted to steal items of the store and sell them. He ured me that I wouldn't have anything to do with what he was doing. I would basically have to be the lookout. Sadly, I agreed. He took items such as cheap jeans, shirts, house ware items, and purses. I ended up getting involved by putting things in reach where he could get them. A month later, a loss prevention agent came in and review the surveillance of the store. The noticed him taking the items out of the store and they knew he was a friend of mine because he always bring me lunch at work. So the LP wanted me to help set him up. They wanted me to take the alarms off the items and put them in reach so he could get caught. They had a police officer in the back and some up front waiting for the que. However the police up front arrive to early and he got suspicious and left the items at the store and walked out. The police chased him down and confronted him with the evidence they found and told him he was banned from the store. Then a month later, the district manager and two other LP's I never seen before walked in and told me to come with them. I went into the back office with them and they started asking me how I knew him and how did the whole "sting" worked out. I told them what I wanted them to know and left the me out.. I knew it didn't make it right to help him steal but I didn't take anything out of that store. So then, the agent told me I was lying to him and if I didn't confess that I isted him, they would put me in jail for 5 years. He told me they already knew about me helping him. They told me what I did, but they never showed footage or present any evidence to show my involvement. The agent wanted me to be honest and tell them everything..Once I told them verbally about what happened, they wanted me to write a summary the same way it was told. I complied and tried my best to cooperate with them. They told me that I had three options. (1) Go to jail for 5 years (2) Fire me and ban me from the premises or (3) Pay the restitution for the items stolen. I agreed with the 2nd option. Then the agent asked me how much items did he Bob took from the store. I told them he was about $2000 worth. So the agent tried to come up with an equation about the stolen items. Then he told me to never talk to Bob again about them confronting me in the store. He said if I did, they would come after me and arrest me. A few months later after the incident, I got a letter in the mail from Palmer, Reifler, and ociates. The letter said they were representing Burke's Outlet and they were making me pay a restitution of $42,000!!! They said if I didn't, they would pursue the actions filed against me. Let me set the record straight, yeah what I did was wrong, but I NEVER stole anything out of that store. I never got arrested, it didn't got put on my record, I never went to court, and I most definitely never signed any paper work saying that I had to pay or owed them this huge amount of money. I had 30 days to respond to the letter..so I called the law office and they told me I could make a payment arrangement. Currently, I've already paid them about $1000..If I miss any payments, they call my phone or send me letters threatening me to go to court. I really don't know what to do..but I feel like I'm being taken advantage of considering the fact that Burke's never told me anything about restitution. Am I being swindled?