Shell Sediba has midmonth change of diesel price

Dear Administrator,

I am loyal Shell customer with a V+ card. My nearest town , Polokwane is 50 km away and there are 3 Shell garages to choose from. I usually compare the prices for diesel amongst the garages and for the past few months the Shell Sediba is the cheapest.

To my astonishment I discover that the price for the diesel was adjusted at a time when it is not expected . The price for FuelSave D50 diesel was R21.53/l up to the 23 rd of July and today it is R21.93/l . Slips are available

My question : Is this a normal practice for Shell outlets to do and is it allowed ? I tried to contact the manager or owner of the outlet but I was not successful.

Please let me know where I could get clarity on this matter.

Thank you in advance for your assistance.

Regards, Johannes Grobler