Hello! My labor contract will end on January...

 We would like to inform you that if there is no trusted agreement between you and the employer, then continue working after the end of the old contract and your rights are saved and the contract is unlimited in this way, so you don’t have to be worry. However, if the visa expired and the employer wants to keep you then he shall extend the visa, so the employer shall send a letter to the Residence and Foreign Affairs for the renew.

As below article from UAE Labor Law states:

Article (40):
 If the two parties continue the execution of the contract after the expiration of its original period of the expiration of the job as agreed upon without explicit announcement, the original contract shall deemed to be extended implicitly with the same conditions except for the duration term.