You could have used the pro trial version, unrestricted use for '60 days' before parting with any cash.
You will need to contact sales (at) avast (dot) com with details of where and when it was purchased, etc. Though I don't know what the refund policy is (only an avast user) or if you have to get your refund (if available) from where you purchased, but sales should be able to give the information you seek.