As you did not step in their office and everything was in advance for the service they would offer so they need to inform prior cancellation of the policy and should not charge again as you have already paid for service have not got. Of course, the day of your appointment your mother condition was very bad so might be you have received any call or any information and generally one is not in good state to remember. So before you sue make sure to recall and cross check. They cannot cancel any policy without informing you. If they are doing so you can claim.