Big trouble for first time landlord

[Nahal Beckam]

Hello, we rented our house to a coupe claiming they only had a cat. but now our neighbors are telling me they have a little dog. I by no means allow dogs in my house for so many reasons. I am just very confused and very angry. I dont know how to approach this problem. I had to turn down many requests and much higher offers for my rental because they had dogs. now these intruders brought a dog without my permission. what should I do? please help