Anytime you have an issue after work was done on your car it’s always a good idea to take it back to the place that worked on it, this gives them the opportunity to correct it and puts you on record as having a problem after they did work just in case it comes up at a later date.
That said it’s hard to say if the problems are related if I’m honest as most brake problems involve the brakes and not the suspension but on occation you will find brake problems caused by loose suspension parts. Given the age of the vehicle however I don’t think this is likely unless it’s been in an accedent of some sort and things down there needed to be repaired or replaced.
Honestly if it’s still under warranty I would take it perhaps to another dealer to be looked at if your not satisfied with the one you have.