A guy scammed me, but he gave me a bank account number & routing number. Can I use that to take out what he owes me?

Go to small claims court and get a judgement against him. Once you have this in hand and if that account is still active, then you are in your rights to collect any way you can. Also, file charges. If this was a scam, a finding of fraud against him will be a hammer in court to get a judgement against him.