Playing RO hardly uses any data at all, but updating has the potential to since some updates can be hundreds of megabytes.
250GB a month is a lot, though. That's like DL'ing the client 250 times in a month or 200-300 movies in a month. It's 1/4 of a terabyte. You guys have nothing to worry about. ...Unless someone misread something somewhere and it's really 25GB/mo. In that case, it's best to not pirate too much. Much more honest to pay for things anyway.
You should watch it, though, because YouTube uses a surprising amount of data at higher resolutions.