If your previous company hasn't provided you with NOC, it means you are banned for 2 years. This ban has nothing to do with your clean record. After completing 2 years outside Qatar, you can come back for work again.
I think its better that you tell the current company that hired you about this. They will come to know of that anyway while processing your papers for RP. If told, they may be able to secure NOC for you from your previous employer.
If your previous company hasn't provided you with NOC, it means you are banned for 2 years. This ban has nothing to do with your clean record. After completing 2 years outside Qatar, you can come back for work again.
I think its better that you tell the current company that hired you about this. They will come to know of that anyway while processing your papers for RP. If told, they may be able to secure NOC for you from your previous employer.