Importing Contacts to Update Category

I have been attempting to import a list of contacts into Netsuite to try to associate with each contact a specific Contact Category which already exists in Netsuite. I have tried importing Leads and Contacts together as Add or Update, Add, and Update. I have tried importing Contacts only using First Name, Last Name, Company, and then Category from the right (Netsuite) side and then using the pencil icon to manually select the Category. I keep getting errors such as "Customer Record With this ID Already exists" or "Contact with this name already exists" or "Contact by this name could