Claim approved on 10th April 2015 but still no car

I was instructed by my insurance to take my car to Automagic for repairs after my claim was approved. Firstly, the autoshop made me wait 3 weeks for my car to be booked in. I then sent my car on 23rd April 2015, and was advised that the estimated completion dates is 11 May 2015 but that in the meantime i will be advised of developments. To date i have not received any updates regarding my car. I have called the shop on numerous occassions, of which they take down my details and promise to call me back but have never done so. I called the shop yesterday to find out if i can pick up my car and was advised that my car was just sitting in the shop all these days as they have been waiting for authorisation from my insurer (which letter of authorisation was givent to them on 10th April 2015). I am absolutely livid and am actually not surprised by the bad service as the shop looked like it was not well run and the overall atmosphere was below par. I am so dissapointed by the lack of communication and inconvenience. I have not received any calls or apology from the shop. Instead i have received a false sms this morning stating that they tried contacting me.