Settign status of phone call to 'Completed'

I am trying to set the 'Status' of a phone call (which is being created in an after submit on a contact record)  to be completed.

I have tried many options along the lines of:

var state = new Array(1); 
state['0'] = 'completed';
recordCreated.setFieldValues('status', state);

This errors with invalid refence key.

Is this approach wrong or are the vales of 'completed' / 'scheduled' correct?

Setting other field values on the phone call record is not a problem.
Any help appreciated on this small annoying item. 

Regards

Julian