Penalised for being an existing customer

Can you please tell me why does an existing client pay R150.00 admin fee when upgrading, and you don't charge any sim / reconnection / admin fee to a brand new customer? Existing clients who are wanting to stay with you have to pay, where is the sense in that? So I can cancel instead of upgrading / and then sign up a new contract and incur no cost - or I can go to another provider.....<br> I would like to understand the business logic here