Incorrect Pump calibration at Engen Petrol Stations

I bought my car new in 2012. It has a 55 litre fuel tank. Every time since then I fill my car to the brim when putting in Diesel. For years my car took +/-52 liters when the reserve light comes on. More or less after Covid this went up to between 54 and 56 litres. Last month on the the first click, it was at almost 59 litres! It would have been over 60 litres if I did not stop them. Everytime I complain the owner/manager suggests that I bring a 1 litre bottle to check the pump's correctness!!! So I'm paying for 7 litres of Diesel that I'm not getting... at that time it was R20.35 per litre. Times that with 7... equates to more than R140 additionly that I pay to fill my tank. This was at Engen Cape Gate. Other Engens in Cape Town are the same.