Is it stealing when you use more than allowed on someone else's debit card?

My aunt had one of my grandma's debit cards because her and my mom are my grandma's care takers and they handle her money. My aunt gave the debit card to my delinquent cousin on Friday and told him he could only take out $20. It is now Monday and he has used over $600. He will not answer our calls and he has not come back to the house. My aunt finally put a stop on the card. I'm wondering, is there any reason we can call the cops? He was purposely given the card by his mom but he took out WAY more money than he was told he could. Would that be considered stealing? This isn't the first time he's done this and we are all sick of it. This sounds bad but I'm looking for a legitimate reason to get him busted. He needs the help. Can anyone think of anything?