Paid for License no expiring date

I paid for the software VCE Exam simulator once off payment. I used the application from 2012. I wanted to download my software again to start preparing for my exams. When I tried using the application it said my subscription expired. <br> It seems they have changed how the bill the clients. This should not effect me as I paid for the application before they made the changes. The new billing structure should only effect new clients. They are just refusing to help me and just keep on telling me to pay. The new billing structure makes it impossible for me to afford the application. <br>