Misfuelled and BP Say they are not to be blamed.

I never had a problem with BP garage for their customer relation until recently. I drove into BP garage at 28 Cathcart St. KWT and requested the petrol attendant to fill it up with R200 diesel. As I was about to pay up I saw he was filling with Petrol. I emmidiately stopped him at 2Litres. He was admitted to his mistake and told me that it's no train smash as this had happened before. He added more diesel on top of the petrol and that petrol is mostly used to clean a diesel engine. Stupid me I believed him. After few days my car stopped on the robots and I called a machenic to check it. He told me it the petrol and might have damaged the engine or the whole fuel system. I went straight to BP and met with the manager and the petrol attendant to assist with the incident. I was told that I should this is between me and the petrol attendant and that they would not assist me in any way. I tried involving the lawyers but they are just dodging me and telling me after months that they have a policy that states if the car drives off after being misfuelled, they are not responsible and that if a petrol attendant misfuels a car, they cannot be held responsible for that.