Billing-Disconnecting Service

First off I want to comment and say I love Verizon FIOS. I was recently forced to relocate and terminate my Verizon FIOS service. I fully planed on signing back up with Verizon once I am finished relocating. My complaint is I terminated my service on the 22nd of the month OK. Verizon makes you pay a month in advance so in acuallity wouldn't they owe my the difference? Verizon doesn't seem to think so I received an email telling me I had a balance do on the due date. 

I am a very organized person I pay all my bills on time and in full, when it was explained to me by a customer service representative upon disconnecting my service that I did not have to pay any bill I might receive in the future because Verizon always charges you for service a month ahead of time I said OK fine. Much to my surprise the most recent charges I received stated that I owe a $5 late charge $3.50 internet discount removal $7 Internet bundle removal Totaling:$15.50 and yet some how the bill was $25.67 It appears that I am being charged for the discounts that I originally had that month. I called of course to dispute this nonsense after 15 minutes on the phone it was explained to me that Verizon was actually doing me a favor they tried  telling me that I really would have owed close to $40 dollars but b/c of some customer loyalty $10 discount I only owed $25.67, thank you I learned to add, I was finally able to get them it remove the nonsense late charge of $5 bringing my Imaginary Bill down to $20.67 My real question to Verizon is how can you charge you customers or rather former customers money for disconnecting service? 

Oh and at least they had on record that I returned all my equipment. 

I fully had intentions on continuing to do business with Verizon once I got settled into my new place but having to deal with all this nonsense has left me indecisive on if I will continue to do business with them again.