3 Weeks waiting for phone

My wife sent in her iPhone 5S again as it was not working correctly after 2 repair attempts, we were then told after a few days we would get a replacement. We are still waiting for a replacement 3 weeks later, and the shop say they are waiting for the repair centre and the repair centre say they are waiting for a phone. Could someone please sort this out, its totally unacceptable. We pay for insurance and contract fees on time for what? Nice to know after only 10 years with the same service provider they value your business so much.