Will I have any legal obligation if I leave job before I sign the job offer?

To whom it may concern:

I came here to Dubai on a visit visa. I found a job and started training Dec 22-31.

I officially started working on January 1 but they just gave me a Job Offer from MOHRE on January 11 which was sent only via WhatsApp and I never signed because they did not ask to sign it.

Yesterday, January 17, I decided to not continue working with them as I cannot endure the sickening attitude of my manager.

They told me that I need to serve a 30-day notice period plus I need to pay 6000 DHS because they already processed the visa.

I asked them where is the visa and I told them that I never signed the Job Offer, and they did not reply to me anymore.

Can I immediately leave the job or do I need to render a notice period of 30 days plus the 6000 DHS they are asking?

Is there any legal agreement between us even if I did not sign the job offer?

By the way, my passport is also with me. Please help me enlighten my mind on this situation.

Thank you and more power to your firm.