how do I cancel booking after submitting payment?

I at the request of my pet sitter dropped my dog off for 90 min just to get dog comfortable with pet sitter and her home. before taking my dog she was combed out thoroughly and upon returning she had fleas... I know this because my dog is alergic to fleas and soon after getting bit reacts with bumps on her skin. Upon further investigation we found the dog did in fact have fleas. I no longer feel comfortable with the sitter and the environment.