Its states in the terms of use support issues can take upto 2 business days to resolve. In now way will they rip you off. Also if you have a failed transaction then what usually happens it automatically gets returned to your card/account. It doesnt matter where or how this happens, could be supermarket or online purchase, if something fails it goes into a holding area for want of better explanation, then within 48 hours automated systems can see you didnt get your purchase and it is released back to the customer with can take a few days.
This happened to me at ASDA (supermarket that is part of Wal Mart group) a few Christmases ago. Put my card in the machine at the entertainment desk and they didnt actually press the button on their machine to make it ask for my pin and it timed out. Put it through again and all went fine. Got home and £60 was missing from my bank account, called ASDA and they told me to call the bank, then called the bank and they could see the transaction I.D I had given from the receipt of the failed one it was in this holding area, they released it back to my account and everything was fine.
GoG Terms of service :
http://www.gog.com/en/support/policies/terms_of_use Specifically :
"Support/Help with Orders
For help with any questions governing the use of the site, questions about order, technical issues with games, please refer to our online support page. If you can't find what you're looking for, you can send us a message electronically via the Support pages. You consent to receiving emails from us regarding those inquiries.
We will make every effort to respond to your inquiry within 2 business days."
In placing an order with GoG you are agreeing to their terms of use also.