Depending on the petrol station we may contact them via an app they have installed, or by their telephone.

Each of these can take a bit of time for someone to get to if it is not located next them.

Sometimes if the petrol station is busy they may not be able to get to the phone, in which case you should have the opportunity to try again. There is no harm in trying again immediately as they may not have got to the phone in time and will be able to get it the next time.