i ordered a fizz phone for my daughter and a chip using my account but how do I use the referral code now?
Only the first plan activation in a account can use a referral code.
In order to be able to use a referral code for your daughter you need to open a new account and activating the plan in that account using your referral code
That's unfortunate, but the referral is always before checkout - there's no way to add it after a plan is purchased.
If you want to go through the trouble - cancel and return everything, open a new account and make sure the referral is there before you check out, it's clearly indicated.