Handbrake and Park Break not working

I bought a car at Nissan in May 2018, New Nissan Qashqai 2018 Visia Turbo which was sold by a wonderful sales person Marlon in Kuilsriver Cape Town. In December my car gave me a problem with a battery which I did not understand because it was seven months but I never had issue with the battery againj

Then the rubber on the side doors was tearing off, which I have never had a problem in my previous car. Then last month I stopped dropping someone nearby the car did not want to move. I stood for good 15 minutes the light for park break was on as well as the handbrake was flashing non stop. It did this twice and I was worried coz this other time I was in a dangerous area and the car could move and I had to wait till the flashing disappear. I then decided to take the car to the dealership because I was worried about my car and I was told I need to buy a new battery. I was puzzled because my car is still new to have battery issues but on top of that I did not have the usually things that are battery related but anyway I took it back.

This afternoon my husband drove to N1 City Mall and parked, when he came back the car drove to other cars and luckily the security guard saw this but they could not do much than to try and stop it. Today my husband was lucky because no damages done on the other car that it drove too.

Now the question that I have is that we all know that once the key is taken out from the car immediately release the handbrake automatically switch on but it did not work.Why do want to tell me it is still a battery?

That means now I have a risk of driving to other cars or wall because clearly there's something wrong with my hand break. Hence when the car stop and don't want to move it is because hand break thinks that it still need to hold but the team at Nissan did not discover this

What I want to know who will be responsible for this car if it drive to other cars when I have taken it to Nissan because of my concerns and they told me it's battery

What must I do now with this car?