Yes, I'd go in there but by now I'd be so angry I'd be afraid I was going to do the person bodily harm :-)

I would try calling back whoever referred you to the clinic, told you to call them, and see if you can get an intervention in your behalf with a professional calling to find out what the problem is or when it is best to call or how to get a call-back, etc. Just an inquiry by a professional and "complaint" might wake someone up somewhere.