Dissatisfied with brake pads and discs installed

When i took my car for oil and brake fluid servicing in October 2015, i was offered front and rear brake pads and discs for mahala, and advised that i can only pay for labour ,it sounded too good to be true but I thought why not? Hardly 2/3 weeks, my car started leaking oil, i took it back to them because i didn't understand why my car would leak oil just after they did an oil service, they told me that it wasn't them who caused the leak. I had to pay to repair the leak. And now, hardly 5 months after doing that service and fitting the brake pads, my car is making a sound when i brake , a sign that the brake pad i fitted 5 months ago are finished. I've only traveled less that 20 000 km, how can that be?