The Better Business Bureau issued a consumer warning for one of the nation’s largest bitcoin mining companies that consumers say hasn’t delivered refunds. Cointerra, based in Austin, Texas, had received close to 40 complaints in May, and did not provide a reason to the bureau for the delayed refunds.

Cointerra CEO and founder Ravi Iyengar said the company was working through a significant refund backlog and hadn’t kept the BBB abreast on ongoing issues due to Cointerra’s small staff.