I purchased a certified used BMW from Devon hill B...

I purchased a certified used BMW from Devon hill BMW.
I have been getting a moldy odor from the car air-conditioner vent.
It took the car for servicing multiple times for this problem. They just put some air freshener.
This smell was there in the car at the time I purchase it. I spoke with the cells person salesperson and he said that it's the smell of the cleaner.
I doubt if the car is properly certified.
And planning to take the car again to the dealership. I hope they do something about it this time