Beside all things that went wrong... Hashfast clearly messed it up no doubt - my guess is it will come down to the question:
Refund of "value in" BC or refund of "exact number of" BC.
HashFast are refusing to refund in BTC, we are not even at the stage of determining what amounts of BTC will be refunded. HashFast have indicated in an email sent to customers that the refunds must be in USD. It is important to remain focused on the facts. HashFast agreed to refund in BTC, and now are refusing to refund in BTC.