Buying a train at a station where there is no ticket office

I wanted to buy a train ticket from this Prasa Ticket officer she told me in a very rude manner that i must go get change because its my duty to look for change i stood at that station missed 2 trains and wae late for an interview becoz i had to walk up and down the bridge looking for change from fruit vendors what i dnt under stand y is it my duty to for change when i want to board a train