new clock, doesn't want to work?

Hi, I have a brand new wall clock, battery operated, bought on hols, which hasn't worked properly since i've had it. It was going for anything between 10 mins and 10 hours but then stopped, sometimes restarting by itself, but since returning it to vendor it only works for a matter of minutes. The second hand sometimes flickers back & forth before it stops; the vendor replaced the motor, spacer and second hand and sent it back to me as working but it doesn't want to play. I have tried cleaning terminals and changed battery for Duracell but nothing seems to help & am at wits end; can anyone help, please!!??