Our insurance company was notified by employer payroll deduction was no longer an option for premium payment. Premium increased significantly due to no payroll deduction; we sought other coverage. Wrote insurance company a letter canceling coverage but still received invoices for premium. We did not consider ourselves covered by the company. They say we owe premium because they "continued to cover us" even though no premium payment was coming in. Is this legal? They say they never received notice from employer or our letter.