according to click here
The bandwidth usage for World of Warcraft is as follows:
Download: 6 Kb/s - 360 Kb/min - 21 600 Kb/h - 21,09 Mb/hour
Upload: 3 Kb/s - 180 Kb/min - 10 800 Kb/h - 10,54 Mb/hour
This number could change according to what you are doing in-game, for example, if you are finishing a quest, or are in a crowded area, there will be a much higher transfer rate.
TalkTalk download limit is 40 GB not Mb