reducing the validity of the special tariff voucher

Location/place: Bokaro

Name of company/service: vodafone

Respected Sir,
i want to complaint about the vodafone that the tariff voucher we are recharging have its validity time but i have seen many times that its validity over before its period and when i ask about this problem through customer care than they donot consider it and the they are not ready to compensate the loss. and i am frequently exprincing the problem please solve this