If you did it from one of these 3 companies (Nexway, Digital River, or Avast Store). Follow the instructions clearly.
Nexway: https://avast.nexway.com/
Digital River: https://www.findmyorder.com/sstore?Action=DisplayHomePage&SiteID=findmyor&Locale=en_US
Avast Store: https://store.avast.com/DRHM/store?Action=DisplayCustomerServiceOrderSearchPage&SiteID=avast
As previously mentioned in this post by Eddy and bob3160, submitting an ticket is also another way to solve it.