If you didn't receive an exit visa when you left you will be able to gain entry to Qatar but not be able to leave until your previous employer has issued an exit visa.
If this is not possible then you will have to wait 2 years for the exit visa situation to expire.

I returned to Qatar in 2010 following my earlier return to the UK and my previous employer had not completed the proper paperwork.
It took some days for the exit visa to be produced which resulted in me having to re-arrange flights etc.
I hope this assists.
Regards