Collection of this loan may be statute barred. Suggest not contacting ACC or it's agents, Capita, for fear of inadvertantly acknowledging the debt, and resetting the six year statute of limitations clock. Do get legal advice, and have a solicitor briefed and ready to file a statute of limitations defence should Capita go legal. Also, because there is land involved the statute of limitations might be 12 years, so you do need a solicitor with experience in this area to help you work out your position.
Another question, as this was a business loan, was the loan made to the OP in a personal capacity or to a "Ltd" company that the OP has a connection with?