As per company law and policy,

As per company law and policy, I have been providing manpower to a government department. I have been making payments for the past two months, but I have not received my bills. They are saying that payments will be cleared once every six months. They never mention in contact ,in written I never contact the office I had called many times for Payment I want to cancel the contract due to delayed bill clearance, but the government officials are threatening to blacklist me if I stop making payment