My son needs medical treatment but refuses appointments

Hi all. My autistic son is 17 and has ingrowing toe nails which need an operation. But he is absolutely terrified of medical treatment - even going to a GP is too much for him. We have tried to get advice and support through our GP, who has simply referred us to a hospital for an appointment despite us making it clear that he will be completely resistant to even going for an appraisal. We just don't know what to do and feel like we're failing him as parents. We are keeping his toes as free from infection as possible, but we're stuck not being able to get medical help. It seems none of our GPs really understand autism and medical resistance. The advice we continually get is to distract him during an appointment with an iphone or something, but that doesn't help us to actually get him there or help him understand he needs this treatment and might get seriously ill without it.

Has anyone else any experience of this? 

Thank you so much!