IOCL — Online payment done before GAS price increase but taken increased price

Dear Team,
I booked the INDANE refill on 13/02/21 and made payment online on 14/02/21 at Rs. 745.5. But on 15/02/21 the price was increased to Rs. 795.5 and the distributor forced me to pay the extra Rs. 50(increased amount), otherwise the riffle will not provide.
Why should I provide the increased amount after the payment done.

Please suggest and do the needful ASAP.

Regards,
Sanatan
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