2011 TOYOTA PRIUS

For the past 2 years I've had issues with the ABS, Traction, and Brake lights coming off and on on my dashboard of my 2011 Toyota Prius. Mechanics have replaced various things but have never been able to find the exact problem because the car doesn't either give any codes or it gives codes that don't really say what the exact problem is. I took it to a dealership again today, because not only are those 3 lights on but now the car is beeping continuously, and the dealership told me it was going to be over $5800 to fix the car, that's replacing the brake booster pump and the brake master cylinder, but the only code the car is showing is C1239, no other codes, C1239 is for the rear speed sensor LH. Every time I've had a mechanic/dealership look at the car, they can't find the exact issue and after replacing some parts, they tell me it could be the brake booster pump and the brake master cylinder, when I called toyota corporate about the warranty stuff to cover those being replaced because of the faulty issues that have apparently been acknowledged by toyota, toyota refuses to have the warranty work done, telling me that my car no longer qualifies for that warranty work, although I've never received anything from them talking about this issue in the past. I'm told now the beeping is those two items have completely failed and the car is now unsafe to drive, but it's the only vehicle I have to get to work, etc. The lights will come and go, but stay on more steady now with the beeping sound. Toyota should help to cover this, since they know it's a known defect!