X-boss extorts money

I was working for company "J" for almost 6 years previously. We were in the construction industry and I acquired a additions and alterations job in the airport. I was hired to supervised the job. During this job, my company "J" were employed to do mechanical works.

Along the way, the main contractor approached me to an external works. This external works was not written on the contract agreement between company "J" and the main contractor. He said he wants to pay seperately and not use company "J" for the job. Knowing that my x-company do not have the capabilites of doing the job, I recommended a friend to complete the external works without the knowledge of my x-company; and got the main contractor got the payment of 7.5k through me. I've then shared the cost of the works with myself and the friend.

After a year, I left company "J" to seek better oppurtunities. Around 2 years later, the police contacted me in regards to airports works. They had claimed that I had commited "criminal breach of trust". I was so surprised. I went through the investigations for almost 6 month. Life was so difficult and I could sit down without thinking what is going to happen to me.

In the alleged claim, I found out that the main contractor had refuses to pay the balance of the amount of 7.5k and had claimed that he had given me the money. I was devastated, this is what happens when you are trying to help people and this is what you get. On the virtue, I've explained to the police on the scenarios that had happen during the initial dealings. I proclaimed that I did not use any of company "J" equipments to complete the external works.

After 6 months, the court tribunal / police letter came. I was not charged with anything but was turned to a warning not to commit such works again.

Everything subsides for almost 1.5 years, then I started to have a debt collectors calling me, telling me that I owed company "J" for 11.5k. I was so shocked. I ignored the calls and reported the matter to the police about the harrasement from these debt collectors.

I found out that my x-boss of company "J" is chasing me after the money which I do not owe at all to him. He's been calling all around my friends to get to me. It feels like he is like extorting me for the money which I do not owe in the first place.

I really dont know what to do. Who should I asked for help?