Well,your story does match with mine. I also served my employer for 7 yrs but when i made the decision to go for a new opportunity, it was denied. I did consult few lawyers in Qatar who told me that as per current LABOUR LAW, employer's consent is extremely important in order to get NOC.
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Anyhow, you may consult NATIONAL HUMAN RIGHTS COMMITTEE or go to labour dept along with your latest contract copy and explain them about ur situation. I'm hopeful you might get NOC from them
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Also, tell them about your situation like RAISE IN SALARY, future prospectives, your financial situation back at home etc. These might force them either to accept your request or IF YOU'RE LUCKY, you might get RELEASE TOO
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GOOD LUCK DEAR