Bp Ennerdale cheated me on R300 Petrol

I went to BP Garage at Ennerdale with three bars indicating that I can still drive for 230km with what is left in my petrol tank. So when I arrive there on Friday I pored R300 Petrol at 14H33 pump number 3 assisted by the guy named Aron. Usually what I do when I go to pour petrol I switch of the engine, then Aron poured petrol and I swiped with my debit card and pick 'n pay points. Started the car and left only to see that my petrol Gage is still on three bars as it was when I got there. I then went back to tell him that my petrol Gage did not go up as usual, he said maybe my petrol Gage is not working. He said I must go home and see if it does not adjust. Saturday morning I was there around 8H05 am and was told that these nothing they can do about it because the manager(Vick) is not inn therefore I'll have to come back Monday when his available, I asked if they cant call him and I was told that he does not want to be disturbed when his home. One of the guys asked if I have that particular receipt and I told him I do not have cause apparently that is the one can prove if petrol was poured or not, I told him that I do not have that receipt from the computer that indicate which pump was used, petrol attendant and how many litres poured. When I asking Aron about that receipt he said it is not important I must come Monday when the manager(Vick) is available. Monday morning I went there and I was told that his coming inn around 8H00 so I left, In the afternoon when I go there I was told that I just missed him and they tried to get the receipt and they said that the petrol was poured. When I went there Friday to pour petrol my petrol Gage had three bars with 230km, meaning if the petrol was poured it should have more km to travel. I left there went to Engine and poured R300 petrol came back to Bp to show them that my petrol Gage went up to six bars meaning my petrol Gage is working fine and it even showed that I have 510km. I'm truly convinced that they cheated me and this issue of manager that cannot be disturbed when the is a problem I do not understand. At some stage they said maybe I used the petrol over the weekend, others saying petrol went up, other saying Renault cars are problematic, other saying there was a client that poured R500 and the Gage did not go up and come back to complain and they showed him the receipt and he pored R300 again and only then the Gage went up.

I would appreciate it if this matter can be resolved as I ended up feeling as if I'm trying to cheat.