I recently had the same problem, I was told it was because the security compnany that collects the captured cards from the ATM machines had shifted its HQ and this was causing a delay in the return of cards to the bank. Normally it should only take no more than a week.
I finally got a new ATM card 16 days after my card was captured. I have had several problems with Doha Bank in the last few months mainly caused by their poor system of communication with customers.