Contact a landlord/tenant attorney. You may have a good claim for damages, and attorneys fees.
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In MA a tenant may withold rent, because of uninhabitable conditions or violation of the state sanitary code, but the tenant must meet the conditions and follow the procedure set forth in MGL c. 239 s.8A. I would suggest consulting a Landlord Tenant Attorney. Under the statute, a tenant claiming a defense must pay to the clerk of court the fair value of the use and occupation of the premises less the amount awarded a tenant for any counterclaim or make a deposit of such amount or such installments thereof from time to time as the court may direct, for the occupation of the premises. These funds may be used for repair of the premises and the balance of the funds will be returned to the landlord when all violations have been removed. You also must meet certain other conditions to withold rent. Again, the process is rather complex so I would suggest consulting an attorney.