Bharat Petroleum [BPCL] — Cylinder regulator replacement

I have replaced my cylinder's regulator and they have charged me 472 rupees and have give me a bill for buying a regular. In the same day I have gone to return the regular but the person how was present in the office said he doesn't know about these things let the owner come.Next day I have gone there again but they refused to return it and said the billing has been done so it cannot be returned.And they are not give me the old regular back and saying this regular belongs to government . I have gone to there office 5 to 6 time in this 3 days still they are not responding. This place is a village area so they are misleading people. Adress of the office Teyandul Bharatgas Gramin Vitrak, Vill & Po Teyandul Block Raina Teyandul Pincode-713424