Shell steeling petrol

I went to Shell service station Manaba KZN to fill my 2013 BMW R1200R classic. The rated fuel capacity of the set model is throughout the board in all investigations 18 lt when I had my bike filled witch I will add was empty with a range of 10km to go on the fuel computer took a total off 23.147 lt to fill that is a staggering 5.147 lt that is lost in space. How can that be possible? This is not the first time that I experienced this tipe off malfunction ont Shell petrol pumps. And would like to get a answer.