Your title says they are 12v DC motors!
Are they?
If so how could you imagine they would work properly with a 9v battery?
What sort of 9v battery? A puny PP3 that is not intended to power a motor?
If the L293 burned out is is almost certain that the motor drew too much current.
So what is the stall current of the motor?
What is the current drawn by the motor running with its normal load?
You need a driver board that can handle the stall current without overheating.
How long do you want the motor to run from the battery?
Amps x hrs = Ah. Multiply by 2 to get the required battery capacity with a margin for error and an allowance for the optimism of battery manufacturers.
...R