Extreme Overage Charges

Call 800+288+2020, Billing department. Then inform them whats happening they are willing to extend help.

you should've verified the change first with the representative you spoke with before ending the call, it's actually part of the process that the changes will only take effect as to when you called to do such. the fault is kinda from your end, though. crossing t's dotting i's.

And that is where I feel that is AT&T's job. They work there. I do not. I had no idea that they did not back date it. Had he said, I can only make this effective for today, and not the beginning of the bill cycle, and inform me I will still an overage. He told me he suggested the unlimited plan to avoid overages in the future. He didn't clarify in detail what the future was. Again, I do not work there. They need to inform me how it is. I can't know what questions to ask or not ask.

Not to mention, when I called 2 weeks ago, the call was disconnected or ended before I would have had a chance anyway. So, them asking me for a call back number in case we get disconnected is irrelevant. And, I am still on hold with dead air right now. No one is coming back on the line. 

@klown4858 . There is no such thing as backdating.  We're are all the same please tell me a service that do backdating, similar to what we are on. This is Business keep that in mind.

[EDITED per Community Guidelines - keep it courteous]

There is no such thing as backdating don't be entitled.

Actually there is or at least there was. When changing plans in the middle of a bill cycle, one of the options was to backdate the change to the beginning of that bill cycle. I do not know if that option still exists, I haven’t done a plan change in several years.

When I changed plans recently, backdating is no longer available.

The system does not allow the new unlimited plans to be backdated for some reason. 

I know right and this is to be expected, changes here and there along with contracts.