My ex employer is accusing me of picking up stock for delivery for a store and not delivering. I have not picked up any stock. they are threatening action.

Thanks for the response. 
I resigned from my job as retail incharge 2 weeks ago. After i submittedmy resignation, my employer started accusing me of stock discrepancy. They claimed that i did not deliver the stock i had picked up for a certain store. That is not even my job as i am not a delivery person. I was working as a manager. I have not signed any delivery challans. A week after my resignation they are now saying that some staff of theirs told them that i had taken some stock to be shifted from one store to another, but again the store has not received it.
I have already explained to them. They are saying that of i cannot explain the discrepancy they will take action.
What should i do next?

Thanks for the reply. I have already sent them a mail stating the same. They have asked me to visit the office and discuss. Should i go?