This is either a violation or substitution of contract, both of which are not allowed and are with corresponding sanctions or penalties. If you are affected by any of these, you can immediately report to the authorities or file a complaint.
If the violations are gradual or done in bits or pieces, it is advised that you document these incidents either through your personal notes in your diary or through messages
you send out to friends, family or colleagues. If you report these to the employer or recruitment agencies, do not delete or destroy them. These documentations will substantiate or support your complaints and may serve as your evidence when you claim damages or payments.
Please note that even if the violation is done gradually or in bits or pieces, it does not exempt the culprit or violator from any liability or penalty.