A credit is showing up, but never is applied!

We may be one of the few with a 1 GB data plan, but it works well for us. Recently we had an issue where, through no fault of our own our data was eaten up in one day. I called Xfinity and they agreed to waive the $10.00 overage fee and apply it to the next bill. The day the data renewed (back to 0 used) the credit wasn't applied, but displayed as applying to the NEXT billing cycle. Okay, I thought, I'll wait, maybe the credit missed the first billing cycle. Well, December kicks in and now again, the upcoming bill does NOT show the $10.00 credit BUT, now the credit is showing as applying to the JANUARY bill. Humm.....anyone else experiencing a credit that is akin to chasing a rainbow for the pot of gold, only to find the rainbow keeps moving?🌈