Is there any legally sustainable option if one boards a matatu, pays fare, forgets to ask for change, alights and when he/she catches up with the crew a few hours later the makanga insists he gave out all due change....and dares him/her to report to the nearest police station.

.....Also noting that matatus don't issue tickets

No

Refuses with change ....... Accept & move on!!!

Two non-legal but solutions nonetheless

1. Visit the said matatu SACCO and report your grievance to officials
2. Take their official phone numbers and let a policeman friend or lawyer reiterate your position; hoping the change is material to you

There is something called "Nairobi Tax" which everyone must pay at one time or the other. This is to cure the little upumbavus that everyone has when they first come here like thinking that other people are supposed to watch over your things, that everyone is your mother etc. Once you pay it is like getting Chicken Pox you cannot get it again unless you have really low immunity. You will be so much more alert every time hutawai gongwa tena.