Air Austral does not refund travel voucher

My flight to Mauritius was cancelled due to the pandemic. Air Austral issued a voucher and told me I could get a voucher which could be used to book another flight or refunded if not used in a year. After a year, I was told my voucher refund is being processed, I was now told that the agent was already refunded this money. Air Austral issued the voucher and should refund it.