Who should I consult if I want to claim that the contract is invalid? How to sue him? Can someone help me?

Second, the landlord is a tenant and the sovereign is the owner of the house. When issuing a rental contract to the tenant, the tenant should ask the tenant for a copy of the ID card and show the house ownership certificate to see if it is consistent with the ID card before signing the rental contract. Be careful of being cheated!

Once there is a problem, the renter decides that the contract is invalid, and the second landlord insists that the contract is valid, causing losses to the renter. The original owner can take the second landlord to court, and the renter can provide the court with evidence about the house lease contract as the witness of the original owner.