Charges forward or backward?

[#1]

I assume line rental/BB charges are in advance and it's only phone calls that are charged retrospectively. Can you tell me: When my charges are taken from my account early next month, if my service is migrated say middle of my month do I get refunded the rest of the month?
Thank you for my MAC key, by the way, sent to me eleven times on the ticket. OK, already, I got it! 

[#2]

Hi Razer,
Sorry to hear you're leaving. Yes, our billing team will work out if you are owed any subscription charges when you've migrated away. Good luck with your new ISP!

[#3]

Thank you.