can i sue, my vet and non profit agency for breach of contract.

My little dog was taking medication for cushings disease. I had a contract with the vet and non profit agency to give her 3 cushings bloodwork over a year. When i took her in for one in August, left her and was suppose to come back in 3 hrs. When i came back the vet told me she did not do the test, she did a lung xray and said Abby had cancer with 3 weeks to live. Abby never showed signs of cancer, they sent her out to die, did not honor the contract, found out later she should not have been taking the meds they put her on with her cushings meds. 8 months later and bills , I had to put Abby to sleep with conjested heart failure.