Mahanagar Gas — Extra bill receipt

Address:

B- 10/20 2:4 Omkar apartment sec -15 Vashi Navi Mumbai

We have already paid gas bill of Rs 724 in march month but again we received rs 3, 615 bill amount in march month itself and it got expired and then in May we received Rs 5, 068 bill. Can you please tell us why the bill amount is so high and why there were two bills generated in march month?
Was 3615 bill amount added in may month hence the bill for may is so high?