(Reuters) -A company that helps timeshare owners undo their contracts has sued the United States' largest privately held vacation ownership company, accusing Florida-based Westgate Resorts of scheming to eliminate competition for cancellation services. Wesley Financial Group LLC's Orlando federal court lawsuit against Westgate, a subsidiary of Central Florida Investments Inc, claims the company violated federal advertising law and antitrust law. The lawsuit escalates a long-running clash between the two companies in an industry valued at $10.5 billion by industry trade group the American Resort Development Association.