Wrong fuel - Montague branch refuses to pay for their error

I’m a regular at the Montague Drive BP, I fill up there all the time and even grab lunch there on the days I forget to bring lunch to work. I’ve been planning for months to meet up with my parents that had to fly down from up country to come and meet us. So Saturday on our way to meet them I saw my fuel tank is only 1/3 full so decided to put in another R600 so we can make the 5hr trip. I get there, greet the attendant, look him in the eyes and said three times to please put in R600 DIESEL. The inside of the fuel flap also clearly says DIESEL. We made our way a short distance out CT before I felt a slight jolt on the car and decided to pull off immediately and investigate what’s going on. No damage visible so we decided to review the slip and there it was. Unleaded… immediately called the closest BP which was BP Franschoek but they informed me that BP garages cannot help and that I should call a service centres instead. Didn’t want to believe this so I tried calling BP Montague Gardens hoping that they could help us resolve the attendants error - no one picks up the phone. Spent a good 3 hours on the side of the road calling service centres after service centre with no luck, eventually Discovery Insure found a towing company that could at least tow us back home for the weekend. Took the car in for repairs on Monday to Autoworks Milnerton which was amazing, had an affordable quote ready in hours and my car was fixed and ready to go on the road again on Tuesday already. I called BP again Tuesday to tell them the good news that the engine didn’t have any damage to it and it’s just the flush and filters that needed to be paid for and replaces. The manager got very emotional on the phone, yelled at me and then hung up. The total only came to R3641.16 including VAT which I thought was a reasonable price when my friends and family told me how much these type of errors have costed them in the past. Since the amount is below my usual excess my insurance company told me to ask BP directly for the amount payable that I had to put on my own card for now to be able to get my car back from the workshop but BP is handling this extremely unprofessionally and is not being cooperative. Needless to say they lost a loyal customer that will not only avoid that branch from now on but BP as a whole. At least until we can reach some kind of agreement to pay for their error.