Don't forget your consumer law. If the item (car, TV etc) goes faulty in the first 6 months of purchase it is assumed the fault was there when you purchased it, therefore you're entitled to a refund. So the dealer you bought it from should fix this.
If you've bought it on finance (even partially) then you could ring your finance company, explain the situation and tell them "the vehicle isn't fit for purpose" and as such you want to end the finance agreement.
This should get the finance company to get involved and hopefully sort it quicker. As let's be honest, a finance company has a bigger legal team than you or I.
Besides this:
Are the carpets wet? If so could be a leaking heater matrix.
Could be caused by a cracked expansion tank.
Failed expansion tank cap.
Is there any white smoke out of the exhaust?
Is there any mayo looking substance whee you'd put oil in?