Bharat Petroleum [BPCL] — Discourteous Staff - Cheating

Address:

Star Bharat Gas Agency, Ambattur, Chennai

On 11th Dec I raised a complaint[protected] on line stating that the mechanic deputed by them to attend to Gas leakage had charged me exorbitantly for the items replaced by him. No Bill or Receipt was given for the payments. Today one of the lady staff of Star Bharat Gas Agency (my distributor) was speaking to me over phone and responding to my complaint. She was very courteous and polite, but a little later another staff intervened and spoke very rudely to me, even to the extent of threatening me. He disconnected the phone and refused to allow the lady staff to talk to me further.
In my conversation with the lady staff, she confirmed that the mechanic had not only charged me exorbitant rates, but also replaced the Regulator with a duplicate product. It appears that all this is being done with the full connivance of higher ups. As a customer, what is my recourse to justice? Who will redress my grievance and ensure that genuine spares are provided and that all extra charges will be fully refunded to me.? Who will ensure that the system itself has to be set right?