Whats the point of the Online booking system?

I booked online to see Ash @ Douglasdale. When i got there I was seen by someone else as Ash was not there. Although the optometrist was both polite and helpful, he is not Ash. As a client i have the right to see who i want to see - or else there is simply no point to the online booking system. I dont come to Spec savers for Spec Savers, I come to see Ash. I should have been informed that Ash was not going to be there and whether or not I would be comfortable with being attended to by another optometrist. why was i not afforded the choice? Had i known this I would have cancelled.