"Difficulty contacting "

I visited Outpatient on 20 June and received excellent treatment. My problem now, is I need an endoscopy and have unfortunately been given two different dates and times for this, one by phone and one by letter. I have tried several times to contact the department but been unable to speak to anyone and have left several messages but no one has called back. I am now getting extremely stressed as there are only a few days before my appointment and I don’t know which date is correct. Also the booklet which I must read before attending was not enclosed so I have no idea what I should/not do before my appointment. Is it too much to ask that telephone calls are answered?