Indian Oil Corporation [IOC] — cash memo msg amt 656.5 and collected by distributor rs 750

Address: Chennai, Tamil Nadu, 600040

Sir/madam
my cylinder was booked for a refill on 23/10/17. i received a message regarding cash memo [protected] generated of amount rs 656.5 on 27/10/17.
my cylinder was delivered today (1/11/17) with a bill amount of 750. my booking number was 288068.
my distributor is maruti indane disrtibutor.
i want to know why there is a difference in the amount sent in message and invoice. i spoke to the office staff and manager but was not satisfied with their response. kindly look into the matter at the earliest.