Discovery doesn't uphold promises, wastes time

I would like to lodge a formal complaint about the free car wash promotion that was run by Discovery Insure on 18 July.On said date I drove out of my way to BP Queenswood as it was the closest, participating BP as per the terms and conditions distributed by Discovery.When I got there I was stold by the petrol attendant that they were not giving free car washes. I promptly called Discovery where the agent said he would get back to me. 45 minutes later he called me back saying that he couldn't aux out in order to call me back. Please note that 1. I don't care that Discovery makes it difficult for him to do his job and 2) I was told to wait at the petrol station for him to call me back. An hour later the agent called me back saying that I would have to have the car washed and then submit the slip.I'd then get a voucher. So I waited 2 hours at the petrol station for Discovery to firstly not even fix the problem and secondly not uphold the promotion because I'm not sure if Discovery knows this but asking me to pay for the car wassh and then give me a voucher is actually a buy 1 get 1 free deal not a FREE deal which was advertised by Discovery..