The limit for refunds is $50k per billing profile/customer per year so your total of $80k would exceed this limit. You can instead exchange them for other reservations if required.
In terms of how the refund is processed, it will depend on what type of Azure subscription you have. You can read about how these are processed here: https://learn.microsoft.com/en-us/azure/cost-management-billing/reservations/exchange-and-refund-azure-reservations#how-transactions-are-processed