Hi, sorry to read of your inconvenience, we are trying to find out where the problem is.
Please make sure your Internet connection is stable, and go to Avast Mobile Security > Tools > Settings > Subscription. When this screen is displayed, the app should connect to refresh the details about possible licences.
If it doesn't help, please contact our Support by e-mail (android@avast.com), as they have the access to the billing system, will trace your licence and help you restore it. I hope your issue is fixed soon.