Issue with a recently purchased car

Cpu2007

I recently purchased a car from a trader and I also bought extended warranty from the trader for this car(2 years warranty)
2 weeks ago I drove the car on the motorway(a journey of an hour), and on my way back the car grarbox was stiff and sometime it would also not change from 2nd to 3rd gear.
I promptly called my trader and explained the issue; I was told that the service department will call in a day or two but 2 weeks have passed and they keep making excuses(I have called 7-8 times now)
In addition to the fact that I have purchased a warranty, on the documents I've received from the trader, it states that if the car manifests any mechanical electrical problem from the date of purchase, the trader will fix that(the problem with my car occurred within 30 days)
What should I do given that they keep making excuses and saying that they will call me back but they don't (I am only using the car locally as I'm scared that by taking it to the motorway it will get worse)

thank you

bod1467

Well, one option may be to go to the dealer on a busy day (Saturday?), park your car in a really awkward place, then go in and ask loudly "Who can I speak with please about getting my faulty car sorted? I only bought it a couple of weeks ago".

Cpu2007

I would prefer another option, they are wasting my time and I don't want to drive because I'm sure they won't fix or take the car the same day which means that I'll have to take the car back again.