Who plays tricks?

It had been a while since Savannah went to the sanatorium. One day, she received a call from Rainie's attending physician. Originally, Savannah was ready to do the transplant for Rainie. So when she heard what the doctor said, she was really surprised. On the other side of the phone, the doctor informed her, "Hello, Miss Warner? The result of your matching has come out. Thank you very much for your kindness. Although your matching is not suitable, I thank you on behalf of the patient all the same." "You're welcome." After Savannah hung up the phone in puzzlement, she was extremely surprised. What was going on? It was not the first time that she had done the matching for Rainie. Four years ago, her matching was suitable. How could it become not suitable after four years? Did she or Rainie have a genetic mutation in the past four years? Wasn't this a joke? Then, there was only one possibility, that was, the doctor made a mistake! But these doctors were all top experts in Canada. Moreover