Indian Oil Corporation [IOC] — indane - cash memo number change with increased amount

Consumer no - 17226 (Survey park gas service, kolkata -700075)
Gas refill booking date - 19-oct-2018
Cash memo (Memo # [protected]) generated on 26-oct-2018 with amount rs. 907
When the refilled gas cylinder was delivered on 02-nov-2018 the deliver boy gave us different cash memo (Memo # [protected]) with amount rs. 969.5

Generally, the refilled cylinder is delivered within 1-2 days of cash memo generation. This time it took 7 days.

I would like to know why different cash memo number was generated with an increased amount.