Refund pet fee and rent

[Desoon Siu]

I rented out my multi-purpose building 2nd floor to a couple about 9 months ago. They signed lease agreement along with pet Addendum. Now they got split and moved out before the lease ended( they have to pay rent until we find new tenants until the lease ends). So we put our upstair on the market.

Suddenly now they asking their pet fee and rent back, saying it’s ESA dog with doctor’s letter..

What a surprise! 

They never disclosed with me regarding this matter up until now.

What should I do?