That's what you get when you use a shady site.

Its all about common sense. To me that rule shouldnt even be written, and its clear that anybody who reads that first conversation would understand it as the guy simply making a mistake while trying to say "you cant have more than 1 account". I dont think you could exploit that mistake cause literally it means you cant have more than 2 accounts, wich is true, and so it also happens that you cant also have 2 either. At that point you should have asked again "so 2 accounts is ok?" untill he said "yes" or "no". That rule is also implied and anybody with common sense would have assumed that on a website where you buy and sell stuff based on your reputation it is not a normal practise to use 2 diferent accounts, except for scammers that want to use banneable alternative accounts to keep their main protected from bad rep. Im glad they actually have that rule. I think G2A has changed a lot lately, and while its still a bit risky, they got way better, and thats the best you can ask for a website where they sell second hand keys. I dont think this happened because of its shadiness, Anyway, sucks to hear you had trouble with your money, and im glad you didnt lose it. Just in case, when your cash is trapped in some account, you can always buy G2A gift cards (they are sold by G2A, so its guaranteed they will activate properly) and you can activate that card on the other account (wich is something in less shady sites like steam cannot be done, and once you have your credit split in 2 accounts, you are done).

I read the rules once (well, i read only big titles and such, but anyway, i read them once when i wanted to use the site) but, i don't have photographer memory,

Its hard to read them twice instead of annoy an Support member? -.-
You dont had to read the full ToS twice, just the part about multi-account...

Compare this to a Driver-license and an accident: oh sorry officer, i dont have an photographer memory, i did not know its forbidden to cross the street with red lights on :o

Please just stop it. You accepted the TOS when registering, with everything in it, regardless of you read or not. Whatever the support says, as human mistake can be involved, is not superior to TOS. That's like not keeping a real world law because a local lawyer told you otherwise. Yes, support is not exactly good in that case, but you broke a rule that you accepted to hold up when you registered. It's not the support's fault, it's your. The support just made a mistake that enforced your belief that you're doing okay. They are at mistake, but not for the thing you're claiming. And no photographical memory needed to remember rules to " register only one account".
Mistakes happen. Do your best to straighten up with them, but don't act like it's an end of the world we know because they have confusingly worded support, or that you didn't read something. Correct it, learn from it, and don't repeat it. It's such a negligible thing, overblown.
(Btw I don't know if you changed it, but still only one picture in the post, and not an album)