Carry out a negotiation yourself.
Some employers are open to discussion. Colleagues are often able to help with this. If your employer mistreats you or doesn’t pay you however, you should leave. Employers who claim they will pay you later, rarely do.
Ask for help
It can sometimes help if a documented person goes with you to your employers or mediates for you. Mediation often has more chance of success than an official complaint. You may well have to compromise and you need to be able to rely on your employer to keep to the agreement. Your employer’s customers are sometimes also able to exert pressure on your employer.
If you can’t reach an agreement with your employer, the testimony of the mediator can be useful in any subsequent steps.