Legacy plan with 1.2TB cap, $100 overage, and a move coming up

I've been an Xfinity Internet customer for a little over a year. This cycle I backed up my computer, went past the 1.2TB limit, and got hit with the full $100 overage charge.

My understanding is that Xfinity's current internet plans all include unlimited data and the gateway in one price, with a 5-year price guarantee and no term agreement. I signed up right around that transition, so I'm apparently still on an older plan with the cap. There's no option in my account to switch myself over.

Two things I'd like help with:

1. Moving me off the legacy plan onto a current everyday-pricing tier with unlimited data, the gateway, and the 5-year price guarantee. No term agreement.
2. Whether a courtesy credit applies to this cycle's $100 charge.

For context, I'm relocating within the next month or two and will be deciding then whether to transfer service or set up with a different provider at the new address. I'd rather stay with Xfinity, but the data cap is the deciding factor, since large backups and file transfers are a regular part of my work. Getting this resolved before the move would make that an easy decision.

Happy to DM account details. Thanks.