LemonTorque: The day after entering the details of a new credit card on GOG, my bank locked the account due to a suspicious purchase ([url moderated]) originating in Cyprus, where I understand GOG process their card payments. This seems like a very suspicious coincidence and I will no longer trust GOG with my card details.
I recommend using the safer payment options if you're concerned by this.
Please keep in mind that purchasing titles from a key reseller can cause this issue. A lot of times these keys have been acquired illegally and therefore are being revoked in due time, causing your account to be flagged. Please reach out to support if there are any further issues. I will be closing this thread now :)