Drivers charging what they want.

Good day<br> I travel with the bus on certain occasions to work. I get up at the bus station by Elsies bridge in Voortrekker road and take the bus to Montague Gardens. Every time there is a different rate? The driver told me its R18.20 from there to Montague gardens, and R8.00 if you get on in Vasco. I walked to Vasco boulevard this morning but they still charged me R18.20 and in the afternoon when i travel back i pay R8.00. Its really confusing and i heard other people complain aswell about the different amounts going up and coming down. Golden Arrow doesnt have a fixed rate and that's very unprofessional for a bus service. Does the drivers make up their own amount cause it sure looks like it. I would appreciate it if someone can get back to me regarding this issue so that i know in future what i must pay?