Changes rates upon destination

I booked an Uber for my friend son from San Remo to Bellville the rate showed R138 upon arriving at his destination the rate changed to R204 as his mom does not have money I gave him a R150 the driver got into an argument with her now I would like to know why give me a rate of R138 and in the end change it also bear in mind it's my 1st time using Uber so I have nothing outstanding