few question...

> is your visa canceled because you forget to check it?
> is your visa cancel because your employer cancel it?

answer:

> Q1 - you can contact your employer to have a letter address to POEA & Qatar Embassy. allowing you to travel under a temporary travel visa, stating that it will be renewed upon arriving to doha. (it happen to my relative and it works)

> Q2 - then NO way you can enter doha, using your present visa. NOC is useful only if you are inside doha and looking for a prospect employer, with in the grace period of 2 years.

> note: entering doha with expired visa has no chance... only if you are having tourist visa, visiting visa etc., thats another case.

good luck ...