Have to ask, did the dealer use the term "blown"? That is a vague term that can mean so many things. Is your vehicle amplified or just a head unit? Is everything stock?
Did you inspect the speakers for any tears/rips/broken pieces? Does any of the wiring appear burned or fused? Have you measured the watts flowing to each speaker at different volume settings? You can also measure resistance between terminals on speakers, should be maybe 2-8 and a error message such as OL means it is bad.
It is unusual that 3 out of 4 speakers stopped working, once the above questions are answered there will be more to work from. If measurements are normal then maybe, if you have an amp, it has a defect that punched a high signal out and fried your speakers. That can be tested separately. I wouldn't just replace speakers without finding error if you are positive no one turned volume to 'Ear Buster".
