Other driver's insurance is ignoring my calls - it's been 3 weeks

I was rear-ended at a stoplight 3 weeks ago. Other driver admitted fault at the scene, police report clearly states they were at fault. Their insurer is State Farm. I have the claim number, I call every 2-3 days, and I either get voicemail or a "we're still investigating" message.

My car has $4,200 in damage sitting in a shop. The shop won't release it until payment is arranged and I'm paying for a rental out of pocket at $38/day. I have liability-only on my own policy so i cant just go through mine.

Is there anything i can actually do to force them to respond? It feels like they're just hoping i give up. What are my options here?