Brake pad problems, 3 months into having the car

Bought a pre-owned car in November 2015, I picked it up a day or two after it had gone for service (at 27000k/m). 3 months to having the car and only having done 8000k/m on it, the brake pads and disc needed to be replaced. I had to pay for them to get sorted out, but highly felt like it was ridiculous of me to! There's no way one can have a car for 3 months and have to replace brakes in that short period. The Service manager told me that it could be because of my driving, which is highly absurd!! I only paid for the brakes because I needed the car for work! The sales guy who sold me the car was telling me how they won't be paying for three brake repairs. I'm very disgruntled and even thinking of taking the car back as this is bad customer service! I wonder if he brakes were checked to see if they'd make it to the next service; coz if they were, they'd know whether to replace them or not prior to me getting the car.