How do I contact Yahoo about a billing /ordering problem,is there an EMAIL address?

Purchased full version of Beach Head 2000 21/03/08 # 662813. Later purchased Operation victory. #663041 We were billed for BH 2000 again ., so we paid twice. Today tried to purchase "I was an atomic mutant" but the order also includes purchase of BH 2000 yet again..Your advice please.