Thank you for the additional information.
It does not appear you have any legal recourse against the employer unfortunately. I am very sorry to be the bearer of bad news, but since you have no contract and discrimination does not appear to be involved, the employment at will doctrine would permit the employer to change the terms of your employment at any time, or even terminate you altogether without notice.
The bright side is that since the employer's "offer" of a significantly lower wage is not based on any wrongdoing by you, you would normally be entitled to collect unemployment benefits if you refuse the offer and quit.
However, there does not appear to be any basis for seeking compensation for damages against the employer as the law does not protect against this type of conflict and either the employer or employee can terminate the relationship at any time without recourse.
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