If you suspect you are being quietly fired, first determine whether the treatment is specific to you or applicable to all employees. Large-scale lack of promotions or failure to give feedback might signify mismanagement rather than quiet firing unless employers try turning mass layoffs into mass volunteer layoffs. How you approach the situation may vary depending on your company culture and relationship with your bosses.
If you suspect quiet firing, you should not assume that bosses will come to their senses eventually, nor should you resign yourself to the circumstances. The best course of action is to confront the problem directly or indirectly. You could note the observed behaviors and ask managers about the cause. Or, for a more subtle approach, express a desire to move up in the company, and ask for clear instructions. Try to discuss a career plan with your employers, and if you do not gain buy-in or see significant progress on the timeline, then perhaps start seeking new opportunities elsewhere.