Contractor Nightmare

My partner hired a contractor to install HVAC system. Quote was $12,000. We paid deposit of $3000 with personal check.
After removing the furnace + radiators they requested full payment so they could buy new furnace. Despite my advice, my partner paid him. Since we had a HELOC - we paid $12,000 through bank and asked for check to cover deposit.
They finally came back to start installing ductwork and we voiced some concerns (work was sloppy / no permits pulled) and asked to meet/discuss but it was a no call/no show.
Since then his deposit reimbursement check bounced and he’s ghosted us completely. It’s been 2 months. Won’t respond to calls or texts.
So now we’re out $15K, with no heating system in our house. It’s spring, so we aren’t freezing but we need to get this finished before the cold weather approaches.
We plan to file complaint with licensing board and state attorney general but we’re at a loss for what to do next.
Any advice?
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