*****ing my money

I opened up a Mr Price account. Made my first payment of R540, 2 weeks later I go to but and Mr price took R390. I was left with R150. Explain to me how they can deduct so much money. I will never be able to pay it off if they keep doing that. They told me that all the extras will only be R150. So why take R390. That is *****ing!!!! *********. And when i finally get through to talk to someone they transfer me from 1 to the next and then the phone dies. What the hell. Who can afford to pay it like that??????????