petrol not showing

I put in R100 petrol in my car (Kia Picanto) on Monday. my petrol gage works but after putting in the petrol the gage did not move for over 7km, but before that I drove back to the petrol station after I had driven a mere 2km to enquire about the gage not moving. the petrol attendant and the cashier told me that they often have this problem of customers saying that the petrol gage does not indicate immediately. every time I put in petrol in my car, the gage indicates that I've put in petrol. my petrol gage works. the attendant and cashier said they often get customers coming back complaining that they didn't get their petrol but after a while the gage moves. I am concerned customer that they are ok that customers complain about such. the garage manger Philemon was called. he said he will look into the matter, call BP and revert, and today is Thursday, no call. I will never use BP Kew (cnr Corlett dr & 9th Rd, Kew)