My question involves collection proceedings in the State of: texas

I am in the process of selling my home, back in 2006 a creditor filed a judgement against me and I was unaware this had been done. The creditor went out of business and the account was sold to a collection attorney, this attorney went out of business and the subsequent company also went out of business. I cannot find out who bought out the firm and I have tried contacting the company that bought out the original creditor and they have no record of this. ( I may add that this company was sold 3 different times) I can't sell my home until this judgement has been cleared or written off.( expires 9/2016) What can I do on my own to get this removed if there's no one to contact? What are the forms needed to present to the court for this? My home is a homestead.