Hello
Wow sounds scary, your brake shop is right its not the brake pads.
Its most likely the Brake Booster on your car.
When your brake booster fails, then your brake systems fail.
Do you regularly check/change the brake fluid.
Brake fluid should be change every once and while especially during brake pad changes.
If its a faulty brake booster then you have to change it.
Umm try these guys out, i got parts for my car at a really low price. Especially the brake booster its usually expensive so try them out
OEM toyota brake booster discount