"Barnet hospital appointment confirmation letters"

I was sent a letter to ring Barnet Hospital to confirm my appointment in the Dermatology dept. The only phone number provided at the top of the letter isn't the direct number. I was holding on for ages and the person who answered the phone seemed bewildered that I was ringing it and then put me through to the correct number. Please can the correct phone number for the relevant dept be provided in these letters with the suitable times to ring? Thank you.