Then discuss with him and make a written contract. If he does not agree to the contract, then tell him that you will file a collection case against him in court unless he agrees to return the money you guys invested in him.
He was unable to make good with his promise, and he did not mention any modicum of risk when you guys invested in him, right? Kasi if he did and he has evidence, then he will have a valid defense since bitcoin mining has a modicum of risk involved as do all businesses. Wala naman talagang kasiguraduhan sa business, in all honesty.
If things take a turn for the worse and di talaga kayo magkasundo, go to the nearest barangay hall and ask a barangay official to mediate between sa inyo para magkaroon ng kasunduan na tanggap nyong pareho.
Alternatively, you may want to go to the nearest Public Attorney's Office sa may City/Municipal Hall and ask for free legal advice regarding your matter.