I just bought this a week back and had claimed refund about 3 days ago even before this DD. If they do not refund I shall make chargeback on my creditcard. You may also put forward your claim to Avangate.
Since they asked for 300$ upright , and not as a subscription monthly or yearly, it is clear that they already know this mishap wouuld happen sooner or later, and by this time they can amasss as much 300$ as they can get and appear again under a new name.
Hence file your complaint to Avangate immediately, so that they can block payments to this merchant.
If not you can still do a Chargeback on your CC.