I`d forget taking it to work for now then as its stressing you.
Do the van training at home,muzzle it or cage it,no treats or contact until its stopped barking.There are other things you need to be on with to get a grip of this dog,make sure its in a different room when you are eating,never give it any food unless its put in its bowl.When you come in and its glad to see you then you must ignore it immediately,you can be "nice" to it later.Don`t keep talking to it as if its a human,its a dog,it needs a master and it will be all the better for it,and never give it chocolate,it kills them.