You learned of the data cap policy only when you were in danger of exceeding it.... which underscores one of my pet peeves- that being customer communications and the clear attitude of contempt that Cox has for its captive money farms.. that is, the areas that have no choice but Cox for cable TV or high speed internet.
This is not to say that individual customer service reps are like this- I've received some amazing service from some and the moderators here seem cordial enough... but the corporate policy reflects the customer base as the afterthought it clearly is to the company.
Changes in service, rate increases, and the like are either not communicated or are minimally alluded to in the paper bill (if you haven't gone "green") and word of planned maintenance outages is considered "privileged information"... that from a moderator here on these forums.
The key to dealing with this problem seems to be finding out with whom Cox (and other cable giants) reach service agreements over a given area and dealing with them if not cutting the cord entirely. It's an exceedingly bad business model from a customer standpoint and needs to be addressed.