Bad experience with angkot

In Indonesia, when you are outside Jakarta, the most possible public transport to use is angkot. Angkot is able to load 12 people. I use angkot a lot when I was in Makassar. 
I had bad experiences concerning angkot. It happened when I was in Sukabumi, Majalengka and Cirebon. It was not a big issue actually but it was quite bothering. Usually angkot charges 2000 rupiahs for a short distance and 3000 or 4000 rupiahs for long distance.

But in my case, I was with my American friend who look absolutely different from Indonesian people. The angkot driver usually charged me and my friend with 1000 or even 2000 rupiahs more than the actual charge.6 out of 10 angkots we used charged us more than the normal price. When I was in Sukabumi for instance, i have asked the people there how much should I pay for the angkot from hotel to alfamart, the people in hotel said 2000 rupiahs each. So I went to alfamart by myself and the driver charged me 2000 rupiahs. One day after, I went there again with my White American friend. We gave the driver 4000 rupiahs for both of us. But then the driver said that it was not enough, they asked us to pay 6000 rupiahs for two people. As I didn't want to argue just for 2000 rupiahs extra charge, I gave him 2000 rupiahs with my sulky face. This story can be a reference for the white backpacker when coming to Indonesia.