If they had chosen a plan with very little included data allowance it may have h...

If they had chosen a plan with very little included data allowance it may have had high excess usage costs.

Looking at the Telstra Business website[1], their $19/month 1GB plan has an excess usage rate of $0.25 per MB. Yes, megabyte.

For your guess of 796GB that would work out to over $200,000.

Just because it's an excess usage charge, doesn't mean that it's reasonable.