How can I get money back for repairs not done right?

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Got valve cover gasket repair for my 2001 mitsubishi montero...repair not done right now the heaf gasket/s are damaged. Mechanic won't fix it and won't return what I paid him, well over $1,000 dollars. Please advice me on what I can do. There must be a law against thieves like him, that run a business without a license. Thank you