I tried 3 diff. browsers , i tried from site and from in game , nothing worked there was a hiding message that i found out when i pressed *ctrl +a , ctrl + c , ctrl+v on other page* , and was saying that Paymentwall doesn't accept payments via Credit Cards from Greece anymore. Dunno if it was a bug or error .
I did finally purchased the gun from Steam wallet and Thank god there was this option , i would have missed the 35% off if there wasnt this option for me.