Is it permissible for an employer to verbally pay 1500 instead of 2000 in the written contract, along with transportation and housing allowances?

The fundamental principle is that Muslims are bound by their conditions, and Allah has commanded the fulfillment of contracts. If the contract between you and the company owner was concluded by mutual consent, then the contract is binding on both parties, and it is not permissible to revoke it except with your agreement. However, if the declared agreement was not intended, but was necessitated by a compelling reason (such as coercion by the company owner, or your desire to obtain a legitimate objective that could only be achieved through this contract), then the declared contract is a sham and has no effect, and the verbal agreement would be the valid one; based on the saying of the Prophet, peace and blessings be upon him: "And indeed, every person shall have what he intended."