My concern about shell south africa

I was at one of the leading shell petrol station at vaal evaton when my car accidentally caught fire after refilling gas. I got helped with fire extinguisher by one of the petrol attendant. My problem is that I wasn't happy after a week when they issued me with invoice that I have to pay fire extinguishers that they used. The funny part they used only 2 fire extinguishers but they say I must pay for 3 fire extinguishers. I always use that fuel station because it's the nearest. I don't know if they taking advantage that they know me or is it part of safety procedures of shell south africa. I even wrote email enquiring about what I should do but no response. That email was written on the 27th of December 2024 the day I was presented with invoice. Incident happened 22nd of December 2024.