Owner hides behind 6 moths guarantee "policy"

I have a 2011 Ford Figo and last year February Supa Quick Gezina replaced my rear wheel bearings. On Saturday 26 January I took my car back after I heard a wobbling noise from my left wheel when leaving work and also of increasing cabin noise, I was assisted by Chris who is also the owner. When he checked the wheel bearings he told me that the left side is the one causing the noise inside my car and he is almost sure they used a poor quality part when it was replaced and that there is only 6 months guarantee on the parts. He then did a look up on my invoice and the job card and told me that the part they used was one of the best and that he tried what he could but the supplier will not give an extended guarantee. I was not informed about the 6 moths guarantee when I paid on the 24th of February 2018 nor is it displayed anywhere on the invoice. He also didn't explain to me why it will start giving problems after 11 months, he just kept on saying parts have a 6 moths guarantee, when I asked so how will I know if the right side will last he just pulled up his shoulders and said he can't tell me I must wait and see what happens parts only have 6 months guarantee. How is it that the ones fitted by Ford lasted 7 years? I spoke to friends of mine and they told me that there is no way that a wheel bearing will start giving problems after 11 months if it was fitted properly as some wheel bearings last up to 300 000 km's - When it was replaced it was either installed dry, not fastened properly or the wrong part for my car. I don't drive dirt roads, I avoid puddles and potholes and I drive between 80 and 100 km/h on the highway. I refused to pay for a new part and Chris just left. I was advised by one of the technicians to have the part replaced as soon as possible and not decide to drive far. Chris has no clue how to properly communicate with clients and will hide behind 6 moths guarantee on parts than admit that they made a mistake when replacing the wheel bearing.