Legal Question in Landlord & Tenant Law in Michigan

You should be applying each payment to the oldest debt including late fees outstanding. If he paid a rent payment a month late, it was for the month he didn't pay, not the current month during which you received the payment. He has been late every month, because each payment made should have been applied to the month before. When he and his wife signed a "new" lease, why didn't you make him catch up his rent right then? His argument that he started a new lease may be valid, but only because you didn't enforce the rent that was due from the prior lease. Make a list of the months of occupancy, with the corresponding rent payments made. Send it to him, and tell him that he is delinquent for the month he never paid. Alternatively, tell him that he has been paying every month late, so owes a late fee for each month. When a tenant gets behind, and the landlord permit this...it leads to these sorts of problems.