I get so much love from customers when I email them a few days ahead of the renewal and let them know that they're over quota, that I didn't want them to be surprised by the CC bill, and give them an opportunity to pare back down if they want to.

This is one of those areas where "being a good person" is a competitive advantage and drives lots of retention. Plus, after a couple months of this, they'll all upgrade anyway as paring down gets harder and more time-consuming.