set customer name in Case entity from plugin

Hi,

I am trying to set customer in Case records from plugin . It has set but it's name does not update. My scenario is

I have workflow, in workflow case entity is created. I have write a plugin on precreate of Case entity for set customer lookup.When Case is going to create I have set customer name. Customer has set but it's name does not update.

I have tried following code

EntityRefrence objconRefrence=new EntityRefrence("contact",{Guid of contact record})

objconRefrence.Name="{contact name}"

objcontact["customerid"]=objconRefrence;

Can any one help me out , why this type of behavior occur.

Thanks,

Vaib

---vaib