Why did you promise full btc refunds if either:
a. You don't understand the volatility of bitcoin
or
b. You don't hold all btc payments in full in case of refunds.
If HashFast had enough resources to build your machine without your money, we would have simply kept the machines for ourselves and not taken the unnecessary (and risky) step of involving customers.
"Full BTC refunds" means a full refund of the price (which is always denominated in USD) via the exchange medium of BTC.
Unfortunately, the decision of a few disgruntled customers to lawyer up and go the legal route forced HashFast to issue refunds solely in USD.