Since they passed that cost to the consumer, they should be legally required to pay it back to the consumer. A refund on a tariff that the consumer had to pay should not be legally pocketable by the business, that should be legally considered theft or robbery.

It is not the fault of the business, but if they incur more operating costs refunding the money they overcharged on the consumer, then they need to sue the government to be reimbursed for that.