i would definitely write a letter of complaint to the clinic. here the medical centre i am registered with is a teaching practice, so lots of medical students, but we are always asked at the point of booking if we mind being treated by a student or having one sit in. we have the right to say no. here out healthcare system if free (in that it's funded via taxes etc but if you aren't a taxpayer, you still get treated) and even we have the right to be asked in advance. as you pay hard cash, i'd say you have even more right to have treatment you're happy with and to complain if not. after all, it's not JUST your money, it's your health!