I got a gas connection a year ago. I was once asked by the delivery boy for extra money that I refused to give siting the fact that its all inclusive in the bill and he should ask for payment from distributor and not me. Since, then I have never been asked for extra charges from delivery boy.
If the delivery boy doesn't listen, you should complaint to distributor. Even then if no action is taken against the delivery vendor, complaint for the same with required details to company (IOC/HP/BP...) marking a copy to the distributor. Even if that doesn't help, try consumer court.