well, a couple of years ago, there would have been harder to label and shame G2A for their practice without being labelled as a paranoid...
but by the last two years, we have had sufficient number of news, reports, articles proving or explaining their whole shady behavior and their malptractice to NOT be aware about that and keep buying there.
for me, the red flag is raised once dev teams are bankrupting because of the chargebacks occuring because of G2A accompliceness in fraudulent paiments and money washing... when you end up having a head of a dev team sayin he'd rather have his game downloaded illegaly than bought through G2A as it would hurt his studio LESS. I think it is a significant enough statement to make people thingk...
and for the argument "but on G2A it's soooo cheaper"... i remember a couple of years ago buying the handful of AAA games still worthing it at that time, on day one... at cheaper price than on G2A key... but of course, i only purchased shady physical copies from a very minor unknown shady reseller known as... amazon :)
Anyay, regarding op i hope you ill manage to get a solution, but sadly, if it was a G2A revoked key, you wont be able to get the game or a refund from gog support, unless they are very generous (ie: it's not their problem nor responsability, i would think... but i can be wrong). It seems you would have to deal with G2A support, which (imho) may be as innefficient as humble store's support but for different reasons :)
(for HB it is sheer cluelessness and incompetency; for G2A it's more "we know we are doing shady business and we will stand our ground no matter what, because if we start refunding, it's both admittnce of liability despite our previous claims, and we would open the floodgates that would sink our illegal business model and malpractice)