If you don't have a contract with the company, you can quit with one month written notice. If your company reduced your salary, it has to be in effect by next month. At that time, your resignation will take effect, just walk away. If the company own you money still, sue them in court. In US, a small claim court handle the claim up to $7,500 per case. The filing fee is $20/case. Lawyers are not allowed to present in the small claim court. The system may be differ in your country, check with the court whether they have the small claim division.

for each has the right to change jobs, except when you are under contract and have to cover a certain obligation before pues cada uno tiene el derecho de cambiar de trabajo, exepto cuando estes bajo un contrato y tengas que cubrir cierta obligacion antes

No boss has the right to refuse your resignation unless there is a contractual bond between you and your company.