Could the petrol pump have dispensed diesel by mistake, or vice versa? I imagine this very rarely happens, but it's not unknown:
https://www.chorleycitizen.co.uk/news/1898868.motorist-claims-tesco-diesel-was-petrol/
Also, another potential spanner in the works if you own a diesel car with AdBlue:
https://www.centretank.com/support/adblue-in-diesel-tank