so i just bought a used copy of galCIVII vanilla on ebay, it's the budget version by Explosiv for the UK 

there's a problem

i had no idea this game required a serial number to operate and install, and neither did i asked the seller on ebay beforehand whether he has the serial number bundled with the game i purchased.

couple hours ago i emailed him and he regret to inform me that there is no serial inside.

so what am i to do? does this i can't even install singleplayer now? it's fine if stardock won't give me a serial as understandably i have indeed purchase a USED copy and stardock has no obligation to provide me new serials for multiplayer, but i had no idea this game required the serial to even install and start singleplayer, so what am i do to?

please help me mate, i appriciate for all of your unconditional help.