No help trying to change prepaid to contract

I took a new contract on the Sony M4 Aqua-in haste I mistakenly didn't click to change prepaid to contract. I then called the call centre because my sim card was not a nano sim sent to me but a micro sim. and I asked if they can send me the nano sim but port my prepaid number to my new contract. the lady was extremely rude. I do not think I should be punished for not clicking on one stupid form. I should have an option to change and this was before my sim is even received. I cannot understand how this is not possible???