Indian Oil Corporation [IOC] — inflated billing

Address:

Chennai, Tamil Nadu, 600041

My lpg consumer no. 31361/cooking gas agency, chennai.
I booked refill on 29.07.2018, acceptance sms recd. At 15.39 hrs.
On 30.07.2018 received sms "cash memo [protected] for rs.770.5, generated for booking no.860240; shall be delivered shortly". On 02.08.2018 at 09.46 hrs received sms "cash memo [protected], generated against ur refill booking 860240 stands cancelled. Reason: empty cylinder not available. Delivery may be reattempted shortly". Contacted the agency and told them as i have not cancelled the booking, the reason stated was wrong and that no deliveryboy called at my address till then. Sent sms confirming the conversation. The manager told me that there was some "system problem" in printing bills and that the delivery would be effected today or tomorrow. Around 2.45 pm received the cylinder along with a fresh cash memo no.[protected] for rs.806/- instead of rs.770.5.
The point is: how can a cash memo generated on 30.07.2018 can be cancelled because of a printer defect on 02.08.2018; why i was made to pay rs.35.5 more because of delay in delivery even three days after cash memo generated. If there was subsequent price increase how would it affect bills generated and cylinders earmarked two days earlier? Kindly enquire and enlighten me. Raghavan c