"Is there anyone who can help with a basic enquiry?"

3 weeks ago I attended a regular eye check in Opthalmology. They recommended a new prescription and said they would write to my GP, however this letter has not been received so they cannot change my prescription and the new eye drops I collected at the hospital will only last another week. I have tried to call during business hours to go through to the opthalmology dept but a recorded message says they are too busy to speak to me. I also tried going through switchboard who kindly put me through to the Consultant's secretary, however this went straight to voicemail. I just need a simple letter delivered to my GP but I seem to have no means of speaking to someone to ensure it happens. I appreciate the department is busy and doesn't want to be swamped with phone calls but there does need to be some way of communicating when the need arises. If the letter has become lost in the post, how would I be able to arrange a duplicate if I can't speak to someone?