Having a copy of the bills means nothing; a CSR can see the same thing. It doesn't discount the fact that you're still not understanding.
To remove a channel, the CSC must select a downgrade date that corresponds with the accounts bill cycle end date.
Since you ask "What 'Bill Cycle'?", I'll explain. You're billed for 1 month at a time. Say your cycle is the 25th of one month to the 24th of the next. If you added a channel on the 1st of a month, you'll be pro rated from that date to the 24th. The soonest you can remove it would be the 24th, which is the date you paid up to. If you decide not to remove it on or before that date, it's billed until the 24th of the next month. This is covered in your Terms of Service as well, if you care to check over those.
I worked all last week; systems weren't updating. The agent told you that because their systems were down, and that's what we're scripted to say. All you had to do was CALL BACK and another agent in one of the other 9 centers would have been able to assist you. Part of the script is "Call back in 2/4 hours" -- if you choose not to, that's not really our fault, is it.
My last point should give you your original answer, since all it seems your concerned about is the charge for another 28 days. If you tell the agent that you spoke with that the previous rep(s) wasn't able to make the change due to their systems "undergoing maintenance", the rep will credit the charge for you, and you get to keep it until the end of your next cycle. Very simple.