Selling unroadworthy vehicles

I had purchased a vehicle from JSN exclusive, the salesman did notify me that the vehicle did need tyres and this would be given to me at no cost to me, the roadworthy certificate dates back two months before the car was purchased and the dealer had put on 2000kms since the report was done, after taking delivery a friend of mine advised me that the vehicle had no thread on the tyres making the car not roadworthy and in an event of an accident I would not be paid out as the tyres are all different brands making the thread all different, also a huge safety issue as this is a performance vehicle, immediately I contacted JSN motors and advised them the issue, they come back to me 4 months later stating they will not accept liability and I should pursue in escalate this to whom I want to, as they are not interested.