"Getting in contact with audiology dept"

I have tried to cancel my sons appointment for the last 4 weeks, I have rung again and again and there has been no-one there to answer. However, it would be better if the dept is unmanned to be able to leave a message on the answerphone, in fact the message states " you cannot leave a message on this telephone" Please can some one tell me how to get in touch with the audiology dept to cancel my appointment so my son is not removed from the register for non attendance?????? its not rocket science - answer phones have been around a long time!!!!!