A carrier can't actually "close" an account until it has a balance of $0.00. What's supposed to happen is that Freedom should have halted your service and stopped billing you for your monthly plan from the day that the number porting was completed. Just make sure when you get your invoice, make sure that they didn't keep charging you. But the prorated partial month's account is a good sign, and you should be fine.
The $5.15 is for the part of the monthly billing cycle from the 2 to 3rd of July that you have already paid for but did not use.
The fact that you can still log into your Freedom Mobile account isn't a bad thing in itself. While some companies immediately lock you out of your online account after you port a number out (cough cough, Rogers/Fido), Freedom may not be doing that. Since your services at Freedom have stopped working and your Public Mobile service is fulling working, that would mean that your number porting is complete. I see this as a convenience thing as this means if you did owe Freedom any money for the last bill, you would still have the convenience of paying online. My experience with Rogers for the few times I ported out from them was that they immediately locked you out of your self-serve account, which meant that if you wanted to make a payment by credit card, you were forced to call them to do it (or make a payment by online banking instead).
