NOC for ex- doha

I worked in doha for almost 2 years and resigned last January... my old company issued me an NOC.
I enter Qatar again last March using tourist visa. The agency who issued me a visit visa valid for 1 month required me to submit my original NOC for the said visa and the application was granted but the NOC was never returned to me... they said it was already forwarded to immigration office.
now, as again im planning to go back to doha for a visit and applying for another visa they are asking me for new original NOC.

I already entered doha for obviously my old sponsor has no objection for me to return and work anytime and try my luck to settle in a decent job.what is the legal procedure for aquiring visa for an ex- doha, do I always have to get NOC everytime I enter Qatar???