Hi,

If you want to make the contact unique, you can do that easily with Automated Actions or Add constraints to the model.

Automated Action

Enable Developer Mode, Then Go to Settings-> Technical -> Automated Actions

Click Create and enter the following:

Model             : Contact
Action To Do  : Execute python code
Active             : True
Trigger           : On Creation & Update

Python Code

if record.name:
  partner = env['res.partner'].search([('id','!=',record.id),('name','=',record.name),('user_id','=',record.user_id.id)])
  if partner:
    raise UserError("Name should be unique")

Constraints

class ResPartner(models.Model):
    _inherit = 'res.partner'
    @api.constrains('name')
    def _check_name(self):
        partner = env['res.partner'].search([('id','!=',self.id),('name','=',self.name),('user_id','=',self.user_id.id)])
        if partner:
            raise UserError("Name should be unique")

Regards