1. HR doesn't work for you; they work to minimize liability for the company. If HR thinks the best way to accomplish that is to destroy your life, that's exactly what they will do.
2. Many SV companies, as well as groups within large, respected SV companies, only survive through exploitation. They exploit their customers, their workforce, or both. Exploitation means obtaining something of value without paying a fair price for it. Exploitation is accomplished through a variety of coercive processes like gaslighting, manipulation, instilling fear, etc. Outright lying is probably the most common coercive tactic since it's easy and there's usually no penalty for it.
If you find yourself in an exploitive work environment, you need to leave as quickly as possible. The situation is not going to get better. It's only going to get worse, and your options are two: Leave with your mental health and reputation intact or leave after they have been destroyed. There is no option 3.