VW POLO TSI with undiagnosed defects sold to a client.

I was sold a VW Polo TSI Life DSG (demo which had travelled just over 13000km) and I heard a strange noise on the day of collection (13 Sep 2024). I informed them about the issue and they booked the car in for inspection, the noise persisted and I took the car back to them for further inspection/repairs. Yet again, they could not diagnose the car and the noise persisted. This happened two more times until they concluded that the noise is normal and that they don't know for how long the noise will persist. I asked them: if the noise is normal, why was this information not disclosed on the day of the test drive? Furthermore, why didn't they confidently say so upon my first complaint? I was told that I cannot get another car, nor could I return the car I have purchased. They sold me a car with issues, they are failing to diagnose or resolve the issue, and I am stuck with the car. I feel taken advantage of and I am frustrated about having to drive a vehicle that has unknown/ undiagnosed defects. Their communication was on point until after I purchased the vehicle from them. I would appreciate any form of advice or assistance.