Spare key not received

I'm a disgruntled customer who has been quite patient with the dealership regarding their bad service.I was sold a car on 27th September 2017 at the Cresta branch and was promised that my spare key will be delivered shortly as it had been misplaced from the branch it was originally from,that being the Woodmead branch.Fast forward to 5 months later after the purchase,I have not yet received my spare key and when I contact them to find out what could be the delay I am sent from pillar to post by staff and branch managers from both branches!!! I am even thinking of opening a case against them as I have tried to follow protocol but I am still without a spare key,I am never going to buy a car from them again and cannot wait until my term ends because I have never received such service since I've owned a car!!!