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There are two options that I see.
The first is to call the police about the vandalism as that is a criminal offence.
The second is to retain a lawyer and have the lawyer send the person a letter demanding they cease and desist, provide a written retraction about the statements made, provide a written apology and threaten a lawsuit for significant damages. Then if that doesn't work your next step would be to sue them for damages.
I hope that helps as a starting point.