RE office wont call back

I've been trying to get in touch with my RE for day 3 bloodwork and ultrasound since they opened Tuesday morning. They emailed me back one time saying I could come Wednesday Thursday or Friday of this week and asked when would be best, I emailed back within 5 minutes to tell them and I've heard nothing at all. I really dont want to have to wait another month just because they will not call me back. I'm on day 3 today so I'm at a lost on what to do. Any suggestions?