Am ashik . Pharmacists i have signed contract with...

Am ashik . Pharmacists i have signed contract with employer to work as a pharmacists. After that he started visa processing and i got visa and also completed medical processes Emirate id process. But unfortunately due to covid 19 took three month time to get medical result and I got medical result and the same day I got another offer from ministry of health umm al quwain to join as a pharmacists in covid 19 field hospital .it was six month contract . So I have called &messaged through wats app and informed about that and he agreed to go. And I have joined in ministry hospital. So am not stamped employment Visa on my passport and not got national id also. The problem now my employers asking money around 4500aed.he told that if i failed to give he will make ban What can I do in such situation. During the period (after contract) he paid any salary. He did not shown full the agreement contract also only one page of the contract given and told to sign . Am first in use so i signed that also . Now how can I get contract copy . What can I do . I wish to work in ministry of health