Avast Free Antivirus old version for windows XP

hi, I have avast free version 2014.9.0.2021 and I use Windows XP sp2 on my PC which is old but it works well. Now the license has expired and I can not register again (the option does not work). The software does not protect my PC. I read that the old versions would continue to do the work. What should I do? thanks for any answers that can solve my problem.
Max