How to find function through call

Hello,

Today I wanted to hack my ammo in Sniper Elite Nazi Zombie Army 2. I realized there is no exact address for that, but for the displayed value. So I have to get the function that writes the value to display. I have the line where the my ammo gets written to the address that is displayed. Before this line there is a call edx instruction. I know this should be the right value, because this is the one that written to the displaying address. So how could I find the function that is giving the correct value of my ammo to the displaying address(call edx)?

Thanks in advance!

Try to analys the game while shooting with CE and it should get you the exact address