https://www.pololu.com/product/3764I've used this one recently, in fact, using the chip right now.
You need to keep the current at a certain level to keep the torque, no current, no torque to hold the motor unfortunately. I think physics has something to do with it...
These are dead simple to use, set the hold current via potentiometer, drive with a pulse, set direction with a pulse. Mode lets you select 1x or 256x steps (that is, 1 pulse is one 256th of a step).
I'm not sure the motor is broken, I just think the holding torque might be just weak.
Cheers,
Alberto