Sandeepthi Gas Agency - Gas delivery boy steels gas cylender

The gas delivery boy from Sandeepthi Gas agency who has been delivering gas cylinder regularly to us came as scheduled two months ago and after delivering the cylender saw a empty cylinder at my place and said that it has crossed the expiry date so it needs to submitted in the office and for next delivery we need not give the empty cylender.
We trusted him as he was regularly visiting us from last three years and gave the cylender to him
After that two times we had booked gas for refil and two times also I got an sms saying that the gas is delivered, however no delivery has bee made, we took the number of the delivery boy and called him.
Today they came to deliver the cylender but the person has changed.
When asked about the earlier guy, they said that he has quit the job and he is no more connected to the company
Moreover, they refused to give the gas as adreed earlier
He called up the godown incharge who very arrogantly replued that he is not concerned with it.
We tried to call up the agency for support but they are not answering the phone.
When we asked for the identity cards of the present people who came to deliver the cylender they couldn't produce it
They also do not have the mechanism to weigh the cylinder, hence we dont know the weight of the cylinder and the content of gas in the cylinder

Hence, request your kind intervention in resolving the issue