Uber *********** the public

Please advise as to why Uber charges change everytime you log into the app?

I have been an avid Uber user for the last 7 months and from my home to my office, 3 months ago the charge for the trip was R22- R24, to my suprise this morning, the first time accessing the app gave me a cost of R57, then R77 and then finally R112. How does Uber charge all these different amounts? So I contact 1 of my employees and ask him to download the Uber app and see what price they get to book an Uber............R39, which is quite a bit less than the amount I was charged as a regular user and so I got my employee to book my Uber.