You need an NOC from your previous Sponsor. As per your post you are still working for the same Company in UAE. Do you think that they will provide you an NOC to leave the job in UAE with them and take a new job in Qatar? If your previous Sponsor was an individual then you should know who is he and you can arrange with someone to go to his Office and request for the NOC. If you were sponsored by your Present Company then you should get it done through them.