Maharashtra Natural Gas [Mngl] — I have paid money twice for a bill

I have paid money twice for a bill. The money has been debited from my account but not been added into the credit. The amount that I paid is 2972. I have been calling the customer care number since last two weeks but no response!!! They are just simply saying that even though you have paid extra money, there's no need to worry as it will be added and stored into the credit and will be used for the next payment. Then, my money should be credited right? Will my money be credited or not ???

The BP number is 50043776
Please look into it